10 Netstat Command Examples

 
Netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc.,
In this article, let us review 10 practical unix netstat command examples.

1. List All Ports (both listening and non listening ports)

List all ports using netstat -a

# netstat -a | more
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:30037         *:*                     LISTEN
udp        0      0 *:bootpc                *:*                                

Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     6135     /tmp/.X11-unix/X0
unix  2      [ ACC ]     STREAM     LISTENING     5140     /var/run/acpid.socket

List all tcp ports using netstat -at

# netstat -at
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:30037         *:*                     LISTEN
tcp        0      0 localhost:ipp           *:*                     LISTEN
tcp        0      0 *:smtp                  *:*                     LISTEN
tcp6       0      0 localhost:ipp           [::]:*                  LISTEN

List all udp ports using netstat -au

# netstat -au
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
udp        0      0 *:bootpc                *:*
udp        0      0 *:49119                 *:*
udp        0      0 *:mdns                  *:*

2. List Sockets which are in Listening State

List only listening ports using netstat -l

# netstat -l
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:ipp           *:*                     LISTEN
tcp6       0      0 localhost:ipp           [::]:*                  LISTEN
udp        0      0 *:49119                 *:*

List only listening TCP Ports using netstat -lt

# netstat -lt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:30037         *:*                     LISTEN
tcp        0      0 *:smtp                  *:*                     LISTEN
tcp6       0      0 localhost:ipp           [::]:*                  LISTEN

List only listening UDP Ports using netstat -lu

# netstat -lu
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
udp        0      0 *:49119                 *:*
udp        0      0 *:mdns                  *:*

List only the listening UNIX Ports using netstat -lx

# netstat -lx
Active UNIX domain sockets (only servers)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     6294     private/maildrop
unix  2      [ ACC ]     STREAM     LISTENING     6203     public/cleanup
unix  2      [ ACC ]     STREAM     LISTENING     6302     private/ifmail
unix  2      [ ACC ]     STREAM     LISTENING     6306     private/bsmtp

3. Show the statistics for each protocol

Show statistics for all ports using netstat -s

# netstat -s
Ip:
    11150 total packets received
    1 with invalid addresses
    0 forwarded
    0 incoming packets discarded
    11149 incoming packets delivered
    11635 requests sent out
Icmp:
    0 ICMP messages received
    0 input ICMP message failed.
Tcp:
    582 active connections openings
    2 failed connection attempts
    25 connection resets received
Udp:
    1183 packets received
    4 packets to unknown port received.
.....

Show statistics for TCP (or) UDP ports using netstat -st (or) -su

# netstat -st

# netstat -su

4. Display PID and program names in netstat output using netstat -p

netstat -p option can be combined with any other netstat option. This will add the “PID/Program Name” to the netstat output. This is very useful while debugging to identify which program is running on a particular port.

# netstat -pt
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        1      0 ramesh-laptop.loc:47212 192.168.185.75:www        CLOSE_WAIT  2109/firefox
tcp        0      0 ramesh-laptop.loc:52750 lax:www ESTABLISHED 2109/firefox

5. Don’t resolve host, port and user name in netstat output

When you don’t want the name of the host, port or user to be displayed, use netstat -n option. This will display in numbers, instead of resolving the host name, port name, user name.
This also speeds up the output, as netstat is not performing any look-up.

# netstat -an

If you don’t want only any one of those three items ( ports, or hosts, or users ) to be resolved, use following commands.

# netsat -a --numeric-ports

# netsat -a --numeric-hosts

# netsat -a --numeric-users

6. Print netstat information continuously

netstat will print information continuously every few seconds.

# netstat -c
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 ramesh-laptop.loc:36130 101-101-181-225.ama:www ESTABLISHED
tcp        1      1 ramesh-laptop.loc:52564 101.11.169.230:www      CLOSING
tcp        0      0 ramesh-laptop.loc:43758 server-101-101-43-2:www ESTABLISHED
tcp        1      1 ramesh-laptop.loc:42367 101.101.34.101:www      CLOSING
^C

7. Find the non supportive Address families in your system

netstat --verbose

At the end, you will have something like this.

 netstat: no support for `AF IPX' on this system.
 netstat: no support for `AF AX25' on this system.
 netstat: no support for `AF X25' on this system.
 netstat: no support for `AF NETROM' on this system.

8. Display the kernel routing information using netstat -r

# netstat -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.1.0     *               255.255.255.0   U         0 0          0 eth2
link-local      *               255.255.0.0     U         0 0          0 eth2
default         192.168.1.1     0.0.0.0         UG        0 0          0 eth2

Note: Use netstat -rn to display routes in numeric format without resolving for host-names.

9. Find out on which port a program is running

# netstat -ap | grep ssh
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
tcp        1      0 dev-db:ssh           101.174.100.22:39213        CLOSE_WAIT  -
tcp        1      0 dev-db:ssh           101.174.100.22:57643        CLOSE_WAIT  -

Find out which process is using a particular port:

# netstat -an | grep ':80'

10. Show the list of network interfaces

# netstat -i
Kernel Interface table
Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0       1500 0         0      0      0 0             0      0      0      0 BMU
eth2       1500 0     26196      0      0 0         26883      6      0      0 BMRU
lo        16436 0         4      0      0 0             4      0      0      0 LRU

Display extended information on the interfaces (similar to ifconfig) using netstat -ie:

# netstat -ie
Kernel Interface table
eth0      Link encap:Ethernet  HWaddr 00:10:40:11:11:11
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
          Memory:f6ae0000-f6b00000

The Ultimate Wget Download Guide With 15 Awesome Examples

wget utility is the best option to download files from internet. wget can pretty much handle all complex download situations including large file downloads, recursive downloads, non-interactive downloads, multiple file downloads etc.,
In this article let us review how to use wget for various download scenarios using 15 awesome wget examples.

1. Download Single File with wget

The following example downloads a single file from internet and stores in the current directory.

$ wget http://www.openss7.org/repos/tarballs/strx25-0.9.2.1.tar.bz2

While downloading it will show a progress bar with the following information:

• %age of download completion (for e.g. 31% as shown below)
• Total amount of bytes downloaded so far (for e.g. 1,213,592 bytes as shown below)
• Current download speed (for e.g. 68.2K/s as shown below)
• Remaining time to download (for e.g. eta 34 seconds as shown below)

Download in progress:

$ wget http://www.openss7.org/repos/tarballs/strx25-0.9.2.1.tar.bz2
Saving to: `strx25-0.9.2.1.tar.bz2.1'

31% [=================> 1,213,592   68.2K/s  eta 34s

Download completed:

$ wget http://www.openss7.org/repos/tarballs/strx25-0.9.2.1.tar.bz2
Saving to: `strx25-0.9.2.1.tar.bz2'

100%[======================>] 3,852,374   76.8K/s   in 55s    

2009-09-25 11:15:30 (68.7 KB/s) - `strx25-0.9.2.1.tar.bz2' saved [3852374/3852374]

2. Download and Store With a Different File name Using wget -O

By default wget will pick the filename from the last word after last forward slash, which may not be appropriate always.
Wrong: Following example will download and store the file with name: download_script.php?src_id=7701

$ wget http://www.vim.org/scripts/download_script.php?src_id=7701

Even though the downloaded file is in zip format, it will get stored in the file as shown below.

$ ls 

download_script.php?src_id=7701

Correct: To correct this issue, we can specify the output file name using the -O option as:

$ wget -O taglist.zip http://www.vim.org/scripts/download_script.php?src_id=7701

3. Specify Download Speed / Download Rate Using wget –limit-rate

While executing the wget, by default it will try to occupy full possible bandwidth. This might not be acceptable when you are downloading huge files on production servers. So, to avoid that we can limit the download speed using the –limit-rate as shown below.
In the following example, the download speed is limited to 200k

$ wget --limit-rate=200k http://www.openss7.org/repos/tarballs/strx25-0.9.2.1.tar.bz2

4. Continue the Incomplete Download Using wget -c

Restart a download which got stopped in the middle using wget -c option as shown below.

$ wget -c http://www.openss7.org/repos/tarballs/strx25-0.9.2.1.tar.bz2

This is very helpful when you have initiated a very big file download which got interrupted in the middle. Instead of starting the whole download again, you can start the download from where it got interrupted using option -c
Note: If a download is stopped in middle, when you restart the download again without the option -c, wget will append .1 to the filename automatically as a file with the previous name already exist. If a file with .1 already exist, it will download the file with .2 at the end.

5. Download in the Background Using wget -b

For a huge download, put the download in background using wget option -b as shown below.

$ wget -b http://www.openss7.org/repos/tarballs/strx25-0.9.2.1.tar.bz2
Continuing in background, pid 1984.
Output will be written to `wget-log'.

It will initiate the download and gives back the shell prompt to you. You can always check the status of the download using tail -f as shown below.

$ tail -f wget-log
Saving to: `strx25-0.9.2.1.tar.bz2.4'

     0K .......... .......... .......... .......... ..........  1% 65.5K 57s
    50K .......... .......... .......... .......... ..........  2% 85.9K 49s
   100K .......... .......... .......... .......... ..........  3% 83.3K 47s
   150K .......... .......... .......... .......... ..........  5% 86.6K 45s
   200K .......... .......... .......... .......... ..........  6% 33.9K 56s
   250K .......... .......... .......... .......... ..........  7%  182M 46s
   300K .......... .......... .......... .......... ..........  9% 57.9K 47s

Also, make sure to review our previous multitail article on how to use tail command effectively to view multiple files.

6. Mask User Agent and Display wget like Browser Using wget –user-agent

Some websites can disallow you to download its page by identifying that the user agent is not a browser. So you can mask the user agent by using –user-agent options and show wget like a browser as shown below.

$ wget --user-agent="Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092416 Firefox/3.0.3" URL-TO-DOWNLOAD

7. Test Download URL Using wget –spider

When you are going to do scheduled download, you should check whether download will happen fine or not at scheduled time. To do so, copy the line exactly from the schedule, and then add –spider option to check.

$ wget --spider DOWNLOAD-URL

If the URL given is correct, it will say

$ wget --spider download-url
Spider mode enabled. Check if remote file exists.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Remote file exists and could contain further links,
but recursion is disabled -- not retrieving.

This ensures that the downloading will get success at the scheduled time. But when you had give a wrong URL, you will get the following error.

$ wget --spider download-url
Spider mode enabled. Check if remote file exists.
HTTP request sent, awaiting response... 404 Not Found
Remote file does not exist -- broken link!!!

You can use the spider option under following scenarios:

• Check before scheduling a download.
• Monitoring whether a website is available or not at certain intervals.
• Check a list of pages from your bookmark, and find out which pages are still exists.

8. Increase Total Number of Retry Attempts Using wget –tries

If the internet connection has problem, and if the download file is large there is a chance of failures in the download. By default wget retries 20 times to make the download successful.
If needed, you can increase retry attempts using –tries option as shown below.

$ wget --tries=75 DOWNLOAD-URL

9. Download Multiple Files / URLs Using Wget -i

First, store all the download files or URLs in a text file as:

$ cat > download-file-list.txt
URL1
URL2
URL3
URL4

Next, give the download-file-list.txt as argument to wget using -i option as shown below.

$ wget -i download-file-list.txt

10. Download a Full Website Using wget –mirror

Following is the command line which you want to execute when you want to download a full website and made available for local viewing.

$ wget --mirror -p --convert-links -P ./LOCAL-DIR WEBSITE-URL

• –mirror : turn on options suitable for mirroring.
• -p : download all files that are necessary to properly display a given HTML page.
• –convert-links : after the download, convert the links in document for local viewing.
• -P ./LOCAL-DIR : save all the files and directories to the specified directory.

11. Reject Certain File Types while Downloading Using wget –reject

You have found a website which is useful, but don’t want to download the images you can specify the following.

$ wget --reject=gif WEBSITE-TO-BE-DOWNLOADED

12. Log messages to a log file instead of stderr Using wget -o

When you wanted the log to be redirected to a log file instead of the terminal.

$ wget -o download.log DOWNLOAD-URL

13. Quit Downloading When it Exceeds Certain Size Using wget -Q

When you want to stop download when it crosses 5 MB you can use the following wget command line.

$ wget -Q5m -i FILE-WHICH-HAS-URLS

Note: This quota will not get effect when you do a download a single URL. That is irrespective of the quota size everything will get downloaded when you specify a single file. This quota is applicable only for recursive downloads.

14. Download Only Certain File Types Using wget -r -A

You can use this under following situations:

• Download all images from a website
• Download all videos from a website
• Download all PDF files from a website

$ wget -r -A.pdf http://url-to-webpage-with-pdfs/

15. FTP Download With wget

You can use wget to perform FTP download as shown below.
Anonymous FTP download using Wget

$ wget ftp-url

FTP download using wget with username and password authentication.

$ wget --ftp-user=USERNAME --ftp-password=PASSWORD DOWNLOAD-URL

15 Practical Linux Top Command Examples

In this article, let us review 15 examples for Linux top command that will be helpful for both newbies and experts.

1. Show Processes Sorted by any Top Output Column – Press O

By default top command displays the processes in the order of CPU usage.  When the top command is running, press M (upper-case) to display processes sorted by memory usage as shown below.

Fig: Press M to sort by memory usage – Unix top command

To sort top output by any column, Press O (upper-case O) , which will display all the possible columns that you can sort by as shown below.

Current Sort Field:  P  for window 1:Def
Select sort field via field letter, type any other key to return 

  a: PID        = Process Id              v: nDRT       = Dirty Pages count
  d: UID        = User Id                 y: WCHAN      = Sleeping in Function
  e: USER       = User Name               z: Flags      = Task Flags
  ........

When the linux top command is running, Press R, which does the sort in reverse order.

2. Kill a Task Without Exiting From Top – Press k

Once you’ve located a process that needs to be killed, press ‘k’ which will ask for the process id, and signal to send.  If you have the privilege to kill that particular PID, it will get killed successfully.

PID to kill: 1309
Kill PID 1309 with signal [15]: 
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1309 geek   23   0 2483m 1.7g  27m S    0 21.8  45:31.32 gagent
 1882 geek   25   0 2485m 1.7g  26m S    0 21.7  22:38.97 gagent
 5136 root    16   0 38040  14m 9836 S    0  0.2   0:00.39 nautilus

3. Renice a Unix Process Without Exiting From Top – Press r

Press r, if you want to just change the priority of the process (and not kill the process). This will ask PID for renice, enter the PID and priority.

PID to renice: 1309
Renice PID 1309 to value: 
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1309 geek   23   0 2483m 1.7g  27m S    0 21.8  45:31.32 gagent
 1882 geek   25   0 2485m 1.7g  26m S    0 21.7  22:38.97 gagent

4. Display Selected User in Top Output Using top -u

Use top -u to display a specific user processes only in the top command output.

$ top -u geek

While unix top command is running, press u which will ask for username as shown below.

Which user (blank for all): geek
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1309 geek   23   0 2483m 1.7g  27m S    0 21.8  45:31.32 gagent
 1882 geek   25   0 2485m 1.7g  26m S    0 21.7  22:38.97 gagent

Display Only Specific Process with Given PIDs Using top -p

Use top -p as shown below to display specific PIDs.

$ top -p 1309, 1882
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1309 geek   23   0 2483m 1.7g  27m S    0 21.8  45:31.32 gagent
 1882 geek   25   0 2485m 1.7g  26m S    0 21.7  22:38.97 gagent

5. Display All CPUs / Cores in the Top Output – Press 1 (one)

Top output by default shows CPU line for all the CPUs combined together as shown below.

top - 20:10:39 up 40 days, 23:02,  1 user,  load average: 4.97, 2.01, 1.25
Tasks: 310 total,   1 running, 309 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.5%us,  0.7%sy,  0.0%ni, 92.3%id,  6.4%wa,  0.0%hi,  0.0%si,  0.0%st

Press 1 (one), when the top command is running, which will break the CPU down and show details for all the individual CPUs running on the system as shown below.

top - 20:10:07 up 40 days, 23:03,  1 user,  load average: 5.32, 2.38, 1.39
Tasks: 341 total,   3 running, 337 sleeping,   0 stopped,   1 zombie
Cpu0  :  7.7%us,  1.7%sy,  0.0%ni, 79.5%id, 11.1%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu1  :  0.3%us,  0.0%sy,  0.0%ni, 94.9%id,  4.7%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu2 :  3.3%us,  0.7%sy,  0.0%ni, 55.7%id, 40.3%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu3 :  5.0%us,  1.0%sy,  0.0%ni, 86.2%id,  7.4%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu4  : 38.5%us,  5.4%sy,  0.3%ni,  0.0%id, 54.8%wa,  0.0%hi,  1.0%si,  0.0%st
Cpu5  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu6  :  0.3%us,  0.7%sy,  0.0%ni, 97.3%id,  1.7%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu7  :  5.4%us,  4.4%sy,  0.0%ni, 82.6%id,  7.7%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu8 :  1.7%us,  1.7%sy,  0.0%ni, 72.8%id, 23.8%wa,  0.0%hi,  0.0%si,  0.0%st

6. Refresh Unix Top Command Output On demand (or) Change Refresh Interval

By default, linux top command updates the output every 3.0 seconds. When you want to update the output on-demand, press space bar.
To change the output update frequency, press d in interactive mode, and enter the time in seconds as shown below.

Change delay from 3.0 to: 10
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1309 geek   23   0 2483m 1.7g  27m S    0 21.8  45:31.32 gagent
 1882 geek   25   0 2485m 1.7g  26m S    0 21.7  22:38.97 gagent

7. Highlight Running Processes in the Linux Top Command Output – Press z or b

Press z or b, which will highlight all running process as shown below.

Fig: Ubuntu Linux – top command highlights running process

8. Display Absolute Path of the Command and its Arguments – Press c

Press c which will show / hide command absolute path, and arguments as shown below.

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1309 geek   23   0 2483m 1.7g  27m S    0 21.8  45:31.32 /usr/sbin/gagent
 1882 geek   25   0 2485m 1.7g  26m S    0 21.7  22:38.97 /usr/sbin/gagent -l 0 -u pre

9. Quit Top Command After a Specified Number of Iterations Using top -n

Until you press q, top continuously displays the output. If you would like to view only a certain iteration and want the top to exit automatically use -n option as shown below.
The following example will show 2 iterations of unix top command output and exit automatically

$ top -n 2

10. Executing Unix Top Command in Batch Mode

If you want to execute top command in the batch mode use option -b as shown below.

$ top -b -n 1

Note: This option is very helpful when you want to capture the unix top command output to a readable text file as we discussed earlier.

11. Split Top Output into Multiple Panels – Press A

To display multiple views of top command output on the terminal, press A. You can cycle through these windows using ‘a’. This is very helpful, when you can sort the output on multiple windows using different top output columns.

12. Get Top Command Help from Command Line and Interactively

Get a quick command line option help using top -h as shown below.

$ top -h
        top: procps version 3.2.0
usage:  top -hv | -bcisS -d delay -n iterations [-u user | -U user] -p pid [,pid ...]

Press h while top command is running, which will display help for interactive top commands.

Help for Interactive Commands - procps version 3.2.0
Window 1:Def: Cumulative mode Off.  System: Delay 3.0 secs; Secure mode Off.

  Z,B       Global: 'Z' change color mappings; 'B' disable/enable bold
  l,t,m     Toggle Summaries: 'l' load avg; 't' task/cpu stats; 'm' mem info
  1,I       Toggle SMP view: '1' single/separate states; 'I' Irix/Solaris mode
  ..........

13. Decrease Number of Processes Displayed in Top Output – Press n

Press n in the Interactive mode, which prompts for a number and shows only that. Following example will display only 2 process as a time.

Maximum tasks = 0, change to (0 is unlimited): 2
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1309 geek   23   0 2483m 1.7g  27m S    0 21.8  45:31.32 gagent
 1882 geek   25   0 2485m 1.7g  26m S    0 21.7  22:38.97 gagent

14. Toggle Top Header to Increase Number of Processes Displayed

By default top displays total number process based on the window height. If you like to see additional process you might want to eliminate some of the top header information.
Following is the default header information provided by top.

top - 23:47:32 up 179 days,  3:36,  1 user,  load average: 0.01, 0.03, 0.00
Tasks:  67 total,   1 running,  66 sleeping,   0 stopped,   0 zombie
Cpu(s):   0.7% user,   1.2% system,   0.0% nice,  98.0% idle
Mem:   1017136k total,   954652k used,    62484k free,   138280k buffers
Swap:  3068404k total,    22352k used,  3046052k free,   586576k cached

• Press l – to hide / show the load average. 1st header line.
• Press t – to hide / show the CPU states. 2nd and 3rd header line.
• Press m – to hide / show the memory information. 4th and 5th line.

15. Save Top Configuration Settings – Press W

If you’ve made any interactive top command configurations suggested in the above examples, you might want to save those for all future top command output. Once you’ve saved the top configuration, next time when you invoke the top command all your saved top configuration options will be used automatically.
To save the top configuration, press W, which will write the configuration files to ~/.toprc. This will display the write confirmation message as shown below.

top - 23:47:32 up 179 days,  3:36,  1 user,  load average: 0.01, 0.03, 0.00
Tasks:  67 total,   1 running,  66 sleeping,   0 stopped,   0 zombie
Cpu(s):   0.7% user,   1.2% system,   0.0% nice,  98.0% idle
Mem:   1017136k total,   954652k used,    62484k free,   138280k buffers
Swap:  3068404k total,    22352k used,  3046052k free,   586576k cached
Wrote configuration to '/home/ramesh/.toprc'

Unix LS Command: 15 Practical Examples

ls – Unix users and sysadmins cannot live without this two letter command. Whether you use it 10 times a day or 100 times a day, knowing the power of ls command can make your command line journey enjoyable.
In this article, let us review 15 practical examples of the mighty ls command.

1. Open Last Edited File Using ls -t

To open the last edited file in the current directory use the combination of ls, head and vi commands as shown below.
ls -t sorts the file by modification time, showing the last edited file first. head -1 picks up this first file.

$ vi first-long-file.txt
$ vi second-long-file.txt

$ vi `ls -t | head -1`
[Note: This will open the last file you edited (i.e second-long-file.txt)]

2. Display One File Per Line Using ls -1

To show single entry per line, use -1 option as shown below.

$ ls -1
bin
boot
cdrom
dev
etc
home
initrd
initrd.img
lib

3. Display All Information About Files/Directories Using ls -l

To show long listing information about the file/directory.

$ ls -l
-rw-r----- 1 ramesh team-dev 9275204 Jun 13 15:27 mthesaur.txt.gz

• 1st Character – File Type: First character specifies the type of the file.
  In the example above the hyphen (-) in the 1st character indicates that this is a normal file. Following are the possible file type options in the 1st character of the ls -l output.
  • Field Explanation
  • - normal file
  • d directory
  • s socket file
  • l link file
• Field 1 – File Permissions: Next 9 character specifies the files permission. Each 3 characters refers to the read, write, execute permissions for user, group and world In this example, -rw-r—– indicates read-write permission for user, read permission for group, and no permission for others.
• Field 2 – Number of links: Second field specifies the number of links for that file. In this example, 1 indicates only one link to this file.
• Field 3 – Owner: Third field specifies owner of the file. In this example, this file is owned by username ‘ramesh’.
• Field 4 – Group: Fourth field specifies the group of the file. In this example, this file belongs to ”team-dev’ group.
• Field 5 – Size: Fifth field specifies the size of file. In this example, ’9275204′ indicates the file size.
• Field 6 – Last modified date & time: Sixth field specifies the date and time of the last modification of the file. In this example, ‘Jun 13 15:27′ specifies the last modification time of the file.
• Field 7 – File name: The last field is the name of the file. In this example, the file name is mthesaur.txt.gz.

4. Display File Size in Human Readable Format Using ls -lh

Use ls -lh (h stands for human readable form), to display file size in easy to read format. i.e M for MB, K for KB, G for GB.

$ ls -l
-rw-r----- 1 ramesh team-dev 9275204 Jun 12 15:27 arch-linux.txt.gz*

$ ls -lh
-rw-r----- 1 ramesh team-dev 8.9M Jun 12 15:27 arch-linux.txt.gz

5. Display Directory Information Using ls -ld

When you use “ls -l” you will get the details of directories content. But if you want the details of directory then you can use -d option as., For example, if you use ls -l /etc will display all the files under etc directory. But, if you want to display the information about the /etc/ directory, use -ld option as shown below.

$ ls -l /etc
total 3344
-rw-r--r--   1 root root   15276 Oct  5  2004 a2ps.cfg
-rw-r--r--   1 root root    2562 Oct  5  2004 a2ps-site.cfg
drwxr-xr-x   4 root root    4096 Feb  2  2007 acpi
-rw-r--r--   1 root root      48 Feb  8  2008 adjtime
drwxr-xr-x   4 root root    4096 Feb  2  2007 alchemist

$ ls -ld /etc
drwxr-xr-x 21 root root 4096 Jun 15 07:02 /etc

6. Order Files Based on Last Modified Time Using ls -lt

To sort the file names displayed in the order of last modification time use the -t option. You will be finding it handy to use it in combination with -l option.

$ ls -lt
total 76
drwxrwxrwt  14 root root  4096 Jun 22 07:36 tmp
drwxr-xr-x 121 root root  4096 Jun 22 07:05 etc
drwxr-xr-x  13 root root 13780 Jun 22 07:04 dev
drwxr-xr-x  13 root root  4096 Jun 20 23:12 root
drwxr-xr-x  12 root root  4096 Jun 18 08:31 home
drwxr-xr-x   2 root root  4096 May 17 21:21 sbin
lrwxrwxrwx   1 root root    11 May 17 20:29 cdrom -> media/cdrom
drwx------   2 root root 16384 May 17 20:29 lost+found
drwxr-xr-x  15 root root  4096 Jul  2  2008 var

7. Order Files Based on Last Modified Time (In Reverse Order) Using ls -ltr

To sort the file names in the last modification time in reverse order. This will be showing the last edited file in the last line which will be handy when the listing goes beyond a page. This is my default ls usage. Anytime I do ls, I always use ls -ltr as I find this very convenient.

$ ls -ltr

total 76
drwxr-xr-x  15 root root  4096 Jul  2  2008 var
drwx------   2 root root 16384 May 17 20:29 lost+found
lrwxrwxrwx   1 root root    11 May 17 20:29 cdrom -> media/cdrom
drwxr-xr-x   2 root root  4096 May 17 21:21 sbin
drwxr-xr-x  12 root root  4096 Jun 18 08:31 home
drwxr-xr-x  13 root root  4096 Jun 20 23:12 root
drwxr-xr-x  13 root root 13780 Jun 22 07:04 dev
drwxr-xr-x 121 root root  4096 Jun 22 07:05 etc
drwxrwxrwt  14 root root  4096 Jun 22 07:36 tmp

8. Display Hidden Files Using ls -a (or) ls -A

To show all the hidden files in the directory, use ‘-a option’. Hidden files in Unix starts with ‘.’ in its file name.

$ ls -a
[rnatarajan@asp-dev ~]$ ls -a
.                             Debian-Info.txt
..                            CentOS-Info.txt
.bash_history                 Fedora-Info.txt
.bash_logout                  .lftp
.bash_profile                 libiconv-1.11.tar.tar
.bashrc                       libssh2-0.12-1.2.el4.rf.i386.rpm

It will show all the files including the ‘.’ (current directory) and ‘..’ (parent directory). To show the hidden files, but not the ‘.’ (current directory) and ‘..’ (parent directory), use option -A.

$ ls -A
Debian-Info.txt               Fedora-Info.txt
CentOS-Info.txt               Red-Hat-Info.txt
.bash_history                 SUSE-Info.txt
.bash_logout                  .lftp
.bash_profile                 libiconv-1.11.tar.tar
.bashrc                       libssh2-0.12-1.2.el4.rf.i386.rpm
[Note: . and .. are not displayed here]

9. Display Files Recursively Using ls -R

$ ls  /etc/sysconfig/networking
devices  profiles

$ ls  -R /etc/sysconfig/networking
/etc/sysconfig/networking:
devices  profiles

/etc/sysconfig/networking/devices:

/etc/sysconfig/networking/profiles:
default

/etc/sysconfig/networking/profiles/default:

To show all the files recursively, use -R option. When you do this from /, it shows all the unhidden files in the whole file system recursively.

10. Display File Inode Number Using ls -i

Sometimes you may want to know the inone number of a file for internal maintenance. Use -i option as shown below to display inone number. Using inode number you can remove files that has special characters in it’s name as explained in the example#6 of the find command article.

$ ls -i /etc/xinetd.d/
279694 chargen      279724 cups-lpd  279697 daytime-udp
279695 chargen-udp  279696 daytime   279698 echo

11. Hide Control Characters Using ls -q

To print question mark instead of the non graphics control characters use the -q option.

ls -q

12. Display File UID and GID Using ls -n

Lists the output like -l, but shows the uid and gid in numeric format instead of names.

$ ls -l ~/.bash_profile
-rw-r--r--  1 ramesh ramesh 909 Feb  8 11:48 /home/ramesh/.bash_profile
$ ls -n ~/.bash_profile
-rw-r--r--  1 511 511 909 Feb  8 11:48 /home/ramesh/.bash_profile

[Note: This display 511 for uid and 511 for gid]

13. Visual Classification of Files With Special Characters Using ls -F

Instead of doing the ‘ls -l’ and then the checking for the first character to determine the type of file. You can use -F which classifies the file with different special character for different kind of files.

$ ls -F
Desktop/  Documents/  Ubuntu-App@  firstfile  Music/  Public/  Templates/

Thus in the above output,

• / – directory.
• nothing – normal file.
• @ – link file.
• * – Executable file

14. Visual Classification of Files With Colors Using ls -F

Recognizing the file type by the color in which it gets displayed is an another kind in classification of file. In the above output directories get displayed in blue, soft links get displayed in green, and ordinary files gets displayed in default color.

$ ls --color=auto
Desktop  Documents Examples firstfile Music  Pictures  Public  Templates  Videos

15. Useful ls Command Aliases

You can take some required ls options in the above, and make it as aliases. We suggest the following.

• Long list the file with size in human understandable form.

  alias ll="ls -lh"

• Classify the file type by appending special characters.

  alias lv="ls -F"

• Classify the file type by both color and special character.

  alias ls="ls -F --color=auto"

Crontab: 15 Awesome Cron Job Examples

 An experienced Linux sysadmin knows the importance of running the routine maintenance jobs in the background automatically.

Linux Cron utility is an effective way to schedule a routine background job at a specific time and/or day on an on-going basis.

Linux Crontab Format

MIN HOUR DOM MON DOW CMD

Table: Crontab Fields and Allowed Ranges (Linux Crontab Syntax)

Field	Description	Allowed Value
MIN	Minute field	0 to 59
HOUR	Hour field	0 to 23
DOM	Day of Month	1-31
MON	Month field	1-12
DOW	Day Of Week	0-6
CMD	Command	Any command to be executed.

1. Scheduling a Job For a Specific Time

The basic usage of cron is to execute a job in a specific time as shown below. This will execute the Full backup shell script (full-backup) on 10th June 08:30 AM.

Please note that the time field uses 24 hours format. So, for 8 AM use 8, and for 8 PM use 20.

30 08 10 06 * /home/ramesh/full-backup

• 30 – 30th Minute
• 08 – 08 AM
• 10 – 10th Day
• 06 – 6th Month (June)
• * – Every day of the week

2. Schedule a Job For More Than One Instance (e.g. Twice a Day)

The following script take a incremental backup twice a day every day.

This example executes the specified incremental backup shell script (incremental-backup) at 11:00 and 16:00 on every day. The comma separated value in a field specifies that the command needs to be executed in all the mentioned time.

00 11,16 * * * /home/ramesh/bin/incremental-backup

• 00 – 0th Minute (Top of the hour)
• 11,16 – 11 AM and 4 PM
• * – Every day
• * – Every month
• * – Every day of the week

3. Schedule a Job for Specific Range of Time (e.g. Only on Weekdays)

If you wanted a job to be scheduled for every hour with in a specific range of time then use the following.

Cron Job everyday during working hours

This example checks the status of the database everyday (including weekends) during the working hours 9 a.m – 6 p.m

00 09-18 * * * /home/ramesh/bin/check-db-status

• 00 – 0th Minute (Top of the hour)
• 09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
• * – Every day
• * – Every month
• * – Every day of the week

Cron Job every weekday during working hours

This example checks the status of the database every weekday (i.e excluding Sat and Sun) during the working hours 9 a.m – 6 p.m.

00 09-18 * * 1-5 /home/ramesh/bin/check-db-status

• 00 – 0th Minute (Top of the hour)
• 09-18 – 9 am, 10 am,11 am, 12 am, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm
• * – Every day
• * – Every month
• 1-5 -Mon, Tue, Wed, Thu and Fri (Every Weekday)

4. How to View Crontab Entries?

View Current Logged-In User’s Crontab entries

To view your crontab entries type crontab -l from your unix account as shown below.

ramesh@dev-db$ crontab -l
@yearly /home/ramesh/annual-maintenance
*/10 * * * * /home/ramesh/check-disk-space

[Note: This displays crontab of the current logged in user]

View Root Crontab entries

Login as root user (su – root) and do crontab -l as shown below.

root@dev-db# crontab -l
no crontab for root

Crontab HowTo: View Other Linux User’s Crontabs entries

To view crontab entries of other Linux users, login to root and use -u {username} -l as shown below.

root@dev-db# crontab -u sathiya -l
@monthly /home/sathiya/monthly-backup
00 09-18 * * * /home/sathiya/check-db-status

5. How to Edit Crontab Entries?

Edit Current Logged-In User’s Crontab entries

To edit a crontab entries, use crontab -e as shown below. By default this will edit the current logged-in users crontab.

ramesh@dev-db$ crontab -e
@yearly /home/ramesh/centos/bin/annual-maintenance
*/10 * * * * /home/ramesh/debian/bin/check-disk-space
~
"/tmp/crontab.XXXXyjWkHw" 2L, 83C

[Note: This will open the crontab file in Vim editor for editing.
Please note cron created a temporary /tmp/crontab.XX... ]

When you save the above temporary file with :wq, it will save the crontab and display the following message indicating the crontab is successfully modified.

~
"crontab.XXXXyjWkHw" 2L, 83C written
crontab: installing new crontab

Edit Root Crontab entries

Login as root user (su – root) and do crontab -e as shown below.

root@dev-db# crontab -e

Edit Other Linux User’s Crontab File entries

To edit crontab entries of other Linux users, login to root and use -u {username} -e as shown below.

root@dev-db# crontab -u sathiya -e
@monthly /home/sathiya/fedora/bin/monthly-backup
00 09-18 * * * /home/sathiya/ubuntu/bin/check-db-status
~
~
~
"/tmp/crontab.XXXXyjWkHw" 2L, 83C

6. Schedule a Job for Every Minute Using Cron.

Ideally you may not have a requirement to schedule a job every minute. But understanding this example will will help you understand the other examples mentioned below in this article.

* * * * * CMD

The * means all the possible unit — i.e every minute of every hour through out the year. More than using this * directly, you will find it very useful in the following cases.

• When you specify */5 in minute field means every 5 minutes.
• When you specify 0-10/2 in minute field mean every 2 minutes in the first 10 minute.
• Thus the above convention can be used for all the other 4 fields.

7. Schedule a Background Cron Job For Every 10 Minutes.

Use the following, if you want to check the disk space every 10 minutes.

*/10 * * * * /home/ramesh/check-disk-space

It executes the specified command check-disk-space every 10 minutes through out the year. But you may have a requirement of executing the command only during office hours or vice versa. The above examples shows how to do those things.

Instead of specifying values in the 5 fields, we can specify it using a single keyword as mentioned below.

There are special cases in which instead of the above 5 fields you can use @ followed by a keyword — such as reboot, midnight, yearly, hourly.

Table: Cron special keywords and its meaning

Keyword	Equivalent
@yearly	0 0 1 1 *
@daily	0 0 * * *
@hourly	0 * * * *
@reboot	Run at startup.

8. Schedule a Job For First Minute of Every Year using @yearly

If you want a job to be executed on the first minute of every year, then you can use the @yearly cron keyword as shown below.

This will execute the system annual maintenance using annual-maintenance shell script at 00:00 on Jan 1st for every year.

@yearly /home/ramesh/red-hat/bin/annual-maintenance

9. Schedule a Cron Job Beginning of Every Month using @monthly

It is as similar as the @yearly as above. But executes the command monthly once using @monthly cron keyword.

This will execute the shell script tape-backup at 00:00 on 1st of every month.

@monthly /home/ramesh/suse/bin/tape-backup

10. Schedule a Background Job Every Day using @daily

Using the @daily cron keyword, this will do a daily log file cleanup using cleanup-logs shell scriptat 00:00 on every day.

@daily /home/ramesh/arch-linux/bin/cleanup-logs "day started"

11. How to Execute a Linux Command After Every Reboot using @reboot?

Using the @reboot cron keyword, this will execute the specified command once after the machine got booted every time.

@reboot CMD

12. How to Disable/Redirect the Crontab Mail Output using MAIL keyword?

By default crontab sends the job output to the user who scheduled the job. If you want to redirect the output to a specific user, add or update the MAIL variable in the crontab as shown below.

ramesh@dev-db$ crontab -l
MAIL="ramesh"

@yearly /home/ramesh/annual-maintenance
*/10 * * * * /home/ramesh/check-disk-space

[Note: Crontab of the current logged in user with MAIL variable]

If you wanted the mail not to be sent to anywhere, i.e to stop the crontab output to be emailed, add or update the MAIL variable in the crontab as shown below.

MAIL=""

13. How to Execute a Linux Cron Jobs Every Second Using Crontab.

You cannot schedule a every-second cronjob. Because in cron the minimum unit you can specify is minute. In a typical scenario, there is no reason for most of us to run any job every second in the system.

14. Specify PATH Variable in the Crontab

All the above examples we specified absolute path of the Linux command or the shell-script that needs to be executed.

For example, instead of specifying /home/ramesh/tape-backup, if you want to just specify tape-backup, then add the path /home/ramesh to the PATH variable in the crontab as shown below.

ramesh@dev-db$ crontab -l

PATH=/bin:/sbin:/usr/bin:/usr/sbin:/home/ramesh

@yearly annual-maintenance
*/10 * * * * check-disk-space

[Note: Crontab of the current logged in user with PATH variable]

15. Installing Crontab From a Cron File

Instead of directly editing the crontab file, you can also add all the entries to a cron-file first. Once you have all thoese entries in the file, you can upload or install them to the cron as shown below.

ramesh@dev-db$ crontab -l
no crontab for ramesh

$ cat cron-file.txt
@yearly /home/ramesh/annual-maintenance
*/10 * * * * /home/ramesh/check-disk-space

ramesh@dev-db$ crontab cron-file.txt

ramesh@dev-db$ crontab -l
@yearly /home/ramesh/annual-maintenance
*/10 * * * * /home/ramesh/check-disk-space

Note: This will install the cron-file.txt to your crontab, which will also remove your old cron entries. So, please be careful while uploading cron entries from a cron-file.txt.

RAID 10 Vs RAID 01 (RAID 1+0 Vs RAID 0+1) Explained with Diagram

RAID 10 is not the same as RAID 01.
This article explains the difference between the two with a simple diagram.
I’m going to keep this explanation very simple for you to understand the basic concepts well. In the following diagrams A, B, C, D, E and F represents blocks.

RAID 10

• RAID 10 is also called as RAID 1+0
• It is also called as “stripe of mirrors”
• It requires minimum of 4 disks
• To understand this better, group the disks in pair of two (for mirror). For example, if you have a total of 6 disks in RAID 10, there will be three groups–Group 1, Group 2, Group 3 as shown in the above diagram.
• Within the group, the data is mirrored. In the above example, Disk 1 and Disk 2 belongs to Group 1. The data on Disk 1 will be exactly same as the data on Disk 2. So, block A written on Disk 1 will be mirroed on Disk 2. Block B written on Disk 3 will be mirrored on Disk 4.
• Across the group, the data is striped. i.e Block A is written to Group 1, Block B is written to Group 2, Block C is written to Group 3.
• This is why it is called “stripe of mirrors”. i.e the disks within the group are mirrored. But, the groups themselves are striped.

If you are new to this, make sure you understand how RAID 0, RAID 1 and RAID 5 and RAID 2, RAID 3, RAID 4, RAID 6 works.

RAID 01

• RAID 01 is also called as RAID 0+1
• It is also called as “mirror of stripes”
• It requires minimum of 3 disks. But in most cases this will be implemented as minimum of 4 disks.
• To understand this better, create two groups. For example, if you have total of 6 disks, create two groups with 3 disks each as shown below. In the above example, Group 1 has 3 disks and Group 2 has 3 disks.
• Within the group, the data is striped. i.e In the Group 1 which contains three disks, the 1st block will be written to 1st disk, 2nd block to 2nd disk, and the 3rd block to 3rd disk. So, block A is written to Disk 1, block B to Disk 2, block C to Disk 3.
• Across the group, the data is mirrored. i.e The Group 1 and Group 2 will look exactly the same. i.e Disk 1 is mirrored to Disk 4, Disk 2 to Disk 5, Disk 3 to Disk 6.
• This is why it is called “mirror of stripes”. i.e the disks within the groups are striped. But, the groups are mirrored.

Main difference between RAID 10 vs RAID 01

• Performance on both RAID 10 and RAID 01 will be the same.
• The storage capacity on these will be the same.
• The main difference is the fault tolerance level. On most implememntations of RAID controllers, RAID 01 fault tolerance is less. On RAID 01, since we have only two groups of RAID 0, if two drives (one in each group) fails, the entire RAID 01 will fail. In the above RAID 01 diagram, if Disk 1 and Disk 4 fails, both the groups will be down. So, the whole RAID 01 will fail.
• RAID 10 fault tolerance is more. On RAID 10, since there are many groups (as the individual group is only two disks), even if three disks fails (one in each group), the RAID 10 is still functional. In the above RAID 10 example, even if Disk 1, Disk 3, Disk 5 fails, the RAID 10 will still be functional.
• So, given a choice between RAID 10 and RAID 01, always choose RAID 10

RAID 2, RAID 3, RAID 4, RAID 6 Explained with Diagram

In most critical production servers, you will be using either RAID 5 or RAID 10.
However there are several non-standard raids, which are not used except in some rare situations. It is good to know what they are.
This article explains with a simple diagram how RAID 2, RAID 3, RAID 4, and RAID 6 works.

RAID 2

• This uses bit level striping. i.e Instead of striping the blocks across the disks, it stripes the bits across the disks.
• In the above diagram b1, b2, b3 are bits. E1, E2, E3 are error correction codes.
• You need two groups of disks. One group of disks are used to write the data, another group is used to write the error correction codes.
• This uses Hamming error correction code (ECC), and stores this information in the redundancy disks.
• When data is written to the disks, it calculates the ECC code for the data on the fly, and stripes the data bits to the data-disks, and writes the ECC code to the redundancy disks.
• When data is read from the disks, it also reads the corresponding ECC code from the redundancy disks, and checks whether the data is consistent. If required, it makes appropriate corrections on the fly.
• This uses lot of disks and can be configured in different disk configuration. Some valid configurations are 1) 10 disks for data and 4 disks for ECC 2) 4 disks for data and 3 disks for ECC
• This is not used anymore. This is expensive and implementing it in a RAID controller is complex, and ECC is redundant now-a-days, as the hard disk themselves can do this.

RAID 3

• This uses byte level striping. i.e Instead of striping the blocks across the disks, it stripes the bits across the disks.
• In the above diagram B1, B2, B3 are bytes. p1, p2, p3 are parities.
• Uses multiple data disks, and a dedicated disk to store parity.
• The disks have to spin in sync to get to the data.
• Sequential read and write will have good performance.
• Random read and write will have worst performance.
• This is not commonly used.

RAID 4

• This uses block level striping.
• In the above diagram B1, B2, B3 are blocks. p1, p2, p3 are parities.
• Uses multiple data disks, and a dedicated disk to store parity.
• Minimum of 3 disks (2 disks for data and 1 for parity)
• Good random reads, as the data blocks are striped.
• Bad random writes, as for every write, it has to write to the single parity disk.
• It is somewhat similar to RAID 3 and 5, but little different.
• This is just like RAID 3 in having the dedicated parity disk, but this stripes blocks.
• This is just like RAID 5 in striping the blocks across the data disks, but this has only one parity disk.
• This is not commonly used.

RAID 6

• Just like RAID 5, this does block level striping. However, it uses dual parity.
• In the above diagram A, B, C are blocks. p1, p2, p3 are parities.
• This creates two parity blocks for each data block.
• Can handle two disk failure
• This RAID configuration is complex to implement in a RAID controller, as it has to calculate two parity data for each data block.

RAID 0, RAID 1, RAID 5, RAID 10 Explained with Diagrams

 RAID stands for Redundant Array of Inexpensive (Independent) Disks.
On most situations you will be using one of the following four levels of RAIDs.

• RAID 0
• RAID 1
• RAID 5
• RAID 10 (also known as RAID 1+0)

This article explains the main difference between these raid levels along with an easy to understand diagram.

In all the diagrams mentioned below:

• A, B, C, D, E and F – represents blocks
• p1, p2, and p3 – represents parity

RAID LEVEL 0

Following are the key points to remember for RAID level 0.

• Minimum 2 disks.
• Excellent performance ( as blocks are striped ).
• No redundancy ( no mirror, no parity ).
• Don’t use this for any critical system.

RAID LEVEL 1

Following are the key points to remember for RAID level 1.

• Minimum 2 disks.
• Good performance ( no striping. no parity ).
• Excellent redundancy ( as blocks are mirrored ).

RAID LEVEL 5

Following are the key points to remember for RAID level 5.

• Minimum 3 disks.
• Good performance ( as blocks are striped ).
• Good redundancy ( distributed parity ).
• Best cost effective option providing both performance and redundancy. Use this for DB that is heavily read oriented. Write operations will be slow.

RAID LEVEL 10

Following are the key points to remember for RAID level 10.

• Minimum 4 disks.
• This is also called as “stripe of mirrors”
• Excellent redundancy ( as blocks are mirrored )
• Excellent performance ( as blocks are striped )
• If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).

DENY SSH LOGIN FOR SOME USERS

Deny SSH access for a specific user

Sometime we required to deny specific user’s SSH access on Linux box due to security reasons.
In this tutorial i am going to show you simple steps for “How to Deny SSH Access for A Specific User”

Step 1:
Login as a root user in order to edit ‘sshd_config’ file. Open this file in vi editor.

vi /etc/ssh/sshd_config

Insert below line in sshd_config file.

DenyUsers  user0 user1 user2

Save and Exit

:wq

Step 2: Now restart ssh service using below command.

Service sshd restart

That’s all

Now user0, user1 and user2 are not allowed to access linux box via ssh

BACKUP IN TAR FORMAT WITH SCRIPT IN CRONTAB

How to backup files and directories in Linux using tar & cron jobs.


Backup Using TAR

Backing up your files using tar is very simple you just type a little command.

#tar -cvpzf   /BackupDirectory/backupfilename.tar.gz  /ImportantData/directory/path


Let’s suppose i have directory called /imp-data on root  and i want to make backup of this directory including sub directories on  different location like in /mybackupfolder.

#tar -cvpzf /mybackupfolder/backup.tar.gz    /imp-data


Command Explaination:
tar = tape archive
c =  Create
v =  Verbose mode
p = Preserving Files and Directory Permissions.
z = This will tell tar that compress the files further to reduce the size of tar file.
f =  It is allows to tar get file name.

Let’s add tar command in bash script to make this whole backup process automatic.
Here i will show you my self-created simple bash script that i am using for backing up my important data and then we will use cron job to run our whole process in background automatically.

Here is my Super Simple Backup Script :)

#vi /backup.sh



#!/bin/bash
#Purpose = Backup of Important Data
#Created on 20-7-2013
#Author = Piyush Gupta
#Version 1.0
#START
TIME=`date +"%b-%d-%y"`         # This Command will add date in Backup File Name. FILENAME="backup-$TIME.tar.gz"     # Here i define Backup file name format. SRCDIR="/imp-data"                 # Location of Important Data Directory
DESDIR="/mybackupfolder"                  # Destination of backup file.
tar -cpzf $DESDIR/$FILENAME $SRCDIR
#END
:wq

#crontab -e

#Minutes Hours Day of Month  Month  Day of Week     Command 01        13        *     *            1,6    /bin/bash       /backup.sh
:wq

#service crond restart
#chkconfig crond on



That’s All… This Script will run at 01:01:00 at every Monday and Saturday.

Linux Directory Structure (File System Structure) Explained with Examples

Have you wondered why certain programs are located under /bin, or /sbin, or /usr/bin, or /usr/sbin?

For example, less command is located under /usr/bin directory. Why not /bin, or /sbin, or /usr/sbin? What is the different between all these directories?

In this article, let us review the Linux filesystem structures and understand the meaning of individual high-level directories.

1. / – Root

• Every single file and directory starts from the root directory.
• Only root user has write privilege under this directory.
• Please note that /root is root user’s home directory, which is not same as /.

2. /bin – User Binaries

• Contains binary executables.
• Common linux commands you need to use in single-user modes are located under this directory.
• Commands used by all the users of the system are located here.
• For example: ps, ls, ping, grep, cp.

3. /sbin – System Binaries

• Just like /bin, /sbin also contains binary executables.
• But, the linux commands located under this directory are used typically by system aministrator, for system maintenance purpose.
• For example: iptables, reboot, fdisk, ifconfig, swapon

4. /etc – Configuration Files

• Contains configuration files required by all programs.
• This also contains startup and shutdown shell scripts used to start/stop individual programs.
• For example: /etc/resolv.conf, /etc/logrotate.conf

5. /dev – Device Files

• Contains device files.
• These include terminal devices, usb, or any device attached to the system.
• For example: /dev/tty1, /dev/usbmon0

6. /proc – Process Information

• Contains information about system process.
• This is a pseudo filesystem contains information about running process. For example: /proc/{pid} directory contains information about the process with that particular pid.
• This is a virtual filesystem with text information about system resources. For example: /proc/uptime

7. /var – Variable Files

• var stands for variable files.
• Content of the files that are expected to grow can be found under this directory.
• This includes — system log files (/var/log); packages and database files (/var/lib); emails (/var/mail); print queues (/var/spool); lock files (/var/lock); temp files needed across reboots (/var/tmp);

8. /tmp – Temporary Files

• Directory that contains temporary files created by system and users.
• Files under this directory are deleted when system is rebooted.

9. /usr – User Programs

• Contains binaries, libraries, documentation, and source-code for second level programs.
• /usr/bin contains binary files for user programs. If you can’t find a user binary under /bin, look under /usr/bin. For example: at, awk, cc, less, scp
• /usr/sbin contains binary files for system administrators. If you can’t find a system binary under /sbin, look under /usr/sbin. For example: atd, cron, sshd, useradd, userdel
• /usr/lib contains libraries for /usr/bin and /usr/sbin
• /usr/local contains users programs that you install from source. For example, when you install apache from source, it goes under /usr/local/apache2

10. /home – Home Directories

• Home directories for all users to store their personal files.
• For example: /home/john, /home/nikita

11. /boot – Boot Loader Files

• Contains boot loader related files.
• Kernel initrd, vmlinux, grub files are located under /boot
• For example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic

12. /lib – System Libraries

• Contains library files that supports the binaries located under /bin and /sbin
• Library filenames are either ld* or lib*.so.*
• For example: ld-2.11.1.so, libncurses.so.5.7

13. /opt – Optional add-on Applications

• opt stands for optional.
• Contains add-on applications from individual vendors.
• add-on applications should be installed under either /opt/ or /opt/ sub-directory.

14. /mnt – Mount Directory

• Temporary mount directory where sysadmins can mount filesystems.

15. /media – Removable Media Devices

• Temporary mount directory for removable devices.
• For examples, /medica/cdrom for CD-ROM; /media/floppy for floppy drives; /media/cdrecorder for CD writer

16. /srv – Service Data

• srv stands for service.
• Contains server specific services related data.
• For example, /srv/cvs contains CVS related data.

LAMP server configration on linux

LAMP is short for Linux, Apache, MySQL, PHP. This tutorial shows how you can install an Apache2 webserver
on an Ubuntu 9.04 server with PHP5 support (mod_php) and MySQL support..
*Installing MySQL 5.0:-
#aptitude install mysql-server mysql-client
You will be asked to provide a password for the MySQL root user – this password is valid for the user root@localhost as well as
root@server1.example.com, so we don’t have to specify a MySQL root password manually later on:
New password for the MySQL “root” user: <– yourrootsqlpassword
Repeat password for the MySQL “root” user: <– yourrootsqlpassword

*Installing Apache2:-

#aptitude install apache2

Now direct your browser to http://192.168.0.100, and you should see the Apache2 placeholder page (It works!):

Apache’s default document root is /var/www on Ubuntu, and the configuration file is /etc/apache2/apache2.conf.
Additional configurations are stored in subdirectories of the /etc/apache2 directory such as /etc/apache2/mods-enabled (for Apache modules), /etc/apache2/sites-enabled (for virtual hosts), and /etc/apache2/conf.d

* Installing PHP5:-

#aptitude install php5 libapache2-mod-php5

We must restart Apache afterwards:
/etc/init.d/apache2 restart

The document root of the default web site is /var/www. We will now create a small PHP file (info.php) in that directory and call it in a browser.
The file will display lots of useful details about our PHP installation, such as the installed PHP version.
# vi /var/www/info.php
<?php
phpinfo();
?>
Now we call that file in a browser (e.g. http://192.168.0.100/info.php):
As you see, PHP5 is working, and it’s working through the Apache 2.0 Handler, as shown in the Server API line. If you scroll further down, you will see all modules that are already enabled in PHP5. MySQL is not listed there which means we don’t have MySQL support in PHP5 yet.

* Getting MySQL Support In PHP5:-

To get MySQL support in PHP, we can install the php5-mysql package. It’s a good idea to install some other PHP5 modules as well as you might need them for your applications. You can search for available PHP5 modules like this:

# aptitude search php5

Pick the ones you need and install them like this:-

aptitude install php5-mysql php5-curl php5-gd php5-idn php-pear php5-imagick php5-imap php5-mcrypt

php5-memcache php5-mhash php5-ming php5-ps php5-pspell php5-recode php5-snmp php5-sqlite php5-tidy php5-xmlrpc php5-xsl php5-json

Now restart Apache2:
/etc/init.d/apache2 restart

Now reload http://192.168.0.100/info.php in your browser and scroll down to the modules section again.

You should now find lots of new modules there, including the MySQL module:

* phpMyAdmin:-

phpMyAdmin is a web interface through which you can manage your MySQL databases. It’s a good idea to install it:

# aptitude install phpmyadmin

You will see the following questions:
Web server to reconfigure automatically: <– apache2
Configure database for phpmyadmin with dbconfig-common? <– No
Afterwards, you can access phpMyAdmin under http://192.168.0.100/phpmyadmin

UPDATE UBUNTU:-
# apt-get install ia32-libs


Download LAMP Source :-http://sourceforge.net/projects/xampp/files/XAMPP%20Linux/

Step by Step Oracle 11g R2 Software Installation & Building the Database

Purpose

This tutorial shows you how to use the Oracle Universal Installer (OUI) to install your Oracle database software and create a starter database. You will also learn how you can use the Database Configuration Assistant (DBCA) to create additional databases.

Time to Complete

Approximately 2 hours

Prerequisites

Before you perform this tutorial, you should:

1.	General computer knowledge.
2.	Familiarity with basic product installs.

Installing the Software Using the Oracle Universal Installer (OUI)

You can use the Oracle Universal Installer (OUI) to install your Oracle software . The OUI is a GUI tool that enables you to view the Oracle software that is installed on your machine, install new Oracle software, and delete Oracle software that you no longer intend to use. There are two methods that you can use to install the Oracle software: basic and advanced. Choose the basic installation method to quickly the install the software with minimal user input. The advanced installation method enables you to perform a custom installation.

A	Basic Installation
B.	Advanced Installation

Basic Installation

Follow the steps below to install the Oracle software and create a database using the basic installation method.

(Note: The Sample Schemas are not installed by default using the Basic Installation option):

1.	Log onto you computer as a member of the administrative group that is authorized to install Oracle software and create and run the database.
2.	Insert the distribution CD for the database into your CD drive. The Autorun window will appear automatically. Note: If you are downloading from Oracle’s download site, follow the instructions given on the Web site.
3.	At the Configure Security Updates window, enter your e-mail address and Oracle Support password and click Next. If you choose to not supply your email address and Oracle Support password, uncheck the check box, leave both text boxes empty, then click Next. When prompted, click Yes.
4.	At the Installation Option window, select Create and configure a database and click Next.
5.	At the System Class window, select Server Class and click Next.
6.	At the Grid Options window, select Single instance database installation and click Next.
7.	At the Install Type window, select Typical install and click Next. Note: If you want to change the database character set to one that supports international languages then perform the Advanced Install starting with step 7.
8.	At the Typical Installation window, enter an Administrative Password. Enter it a second time to confirm the password and click Next. Note that the password is evaluated to make sure that it conforms to Oracle recommended standards. If it is not, you will receive an error window asking if you would like to proceed.
9.	At the Create Inventory window, accept the defaults and click Next.
10.	At the Prerequisite Checks window, you see a list of issues that were not met. Issues which can be resolved by the OUI are listed with Yes in the Fixable column. To allow the OUI to generate a script to fix the fixable issues, click Fix and Check Again.
11.	The Execute Fixup Scripts window will appear, providing instructions.
12.	Open a terminal. Change to the OS user root. Then execute the script. su - root /tmp/CVU_11.2.0.0.2_oracle/runfixup.sh
13.	Return to the Execute Fixup Scripts window and click OK.
14.	At the Summary window, click Finish.
15.	A progress window will appear.
16.	After the software is installed, the Database Configuration Assistant will begin and create your database.
17.	The database was created successfully. Click Close.
18.	You need to execute a couple of scripts as the root user.
19.	Open a terminal window and execute the following commands: su - /u01/app/oraInventory/orainstRoot.sh /u01/app/oracle/product/11.2.0/dbhome_1/root.sh
20.	Return to the Execute Configuration Script window and click OK.
21.	Your installation and database creation completed successfully. click Close.

Advanced Installation

Follow the steps below to install the Oracle software and create a database using the advanced installation method.

Note: If you performed the Basic Installation steps, you do not need to complete this section.

1.	Log onto you computer as a member of the administrative group that is authorized to install Oracle software and create and run the database.
2.	Insert the distribution CD for the database into your CD drive. The Autorun window will appear automatically. Note: If you are downloading from Oracle’s download site, follow the instructions given on the Web site.
3.	At the Configure Security Updates window, enter your e-mail address and Oracle Support password and click Next. If you choose to not supply your email address and Oracle Support password, uncheck the check box, leave both text boxes empty, then click Next. When prompted, click Yes.
4.	At the Installation Option window, select Create and configure a database and click Next.
5.	At the System Class window, select Server Class and click Next.
6.	At the Grid Options window, select Single instance database installation and click Next.
7.	At the Install Type window, select Advanced install and click Next.
8.	At the Product Languages window, select the Move All button to select all the languages.
9.	Click Next.
10.	At the Database Edition window, make sure that Enterprise Edition is selected and click Next.
11.	At the Installation Location window, accept the defaults and click Next.
12.	At the Create Inventory window, accept the defaults and click Next.
13.	At the Configuration Type window, make sure the type of database is set to General Purpose / Transaction Processing and click Next.
14.	At the Database Identifier window, accept the defaults and click Next.
15.	At the Configuration Options window, for the memory tab, you will accept the defaults. Click theCharacter sets tab.
16.	Change the setting to Use Unicode (AL32UTF8) and click the Security tab.
17.	Accept the default and click the Sample Schema tab.
18.	Select the Create database with sample schema check box and click Next.
19.	At the Management Options window, accept the defaults and click Next.
20.	At the Database Storage window, accept the defaults and click Next.
21.	At the Backup and Recovery window, accept the defaults and click Next.
22.	At the Schema Passwords window, select Use the same password for all accounts and enter an Oracle Recommended password and confirm password and click Next.
23.	At the Operating System Groups window, accept the defaults and click Next.
24.	At the Prerequisite Checks window, you see a list of issues that were not met. Issues which can be resolved by the OUI are listed with Yes in the Fixable column. To allow the OUI to generate a script to fix the fixable issues, click Fix and Check Again.
25.	The Execute Fixup Scripts window will appear, providing instructions.
26.	Open a terminal. Change to the OS user root. Then execute the script. su - root /tmp/CVU_11.2.0.0.2_oracle/runfixup.sh
27.	Return to the Execute Fixup Scripts window and click OK.
28.	At the Summary window, click Finish.
29.	A progress window will appear.
30.	After the software is installed, the Database Configuration Assistant will begin and create your database.
31.	The database was created successfully. Click Close.
32.	You need to execute a couple of scripts as the root user.
33.	Open a terminal window and execute the following commands: su - /u01/app/oraInventory/orainstRoot.sh /u01/app/oracle/product/11.2.0/dbhome_1/root.sh
34.	Return to the Execute Configuration Script window and click OK.
35.	Your installation and database creation completed successfully. click Close.

Using the Database Configuration Assistant (DBCA) to Create a Database

If you choose to install software only and later create a database, or if you want to create additional databases using the software that you just installed, you can do so by using the Database Configuration Assistant (DBCA).

Note: If you created a database as part of the Basic Installation or Advanced Installation, you do not need to complete this section.

Follow the steps below to create a new database or a second database if you created a database as part of the software installation:

1.	Log onto your computer as a member of the administrative group that is authorized to install Oracle software and create and manage the database.
2.	Launch the DBCA on a Linux or UNIX operating system by entering the following at a command prompt: dbca
3.	The Welcome window appears. Click Next.
4.	Select Create a Database in the Operations window to begin a process that enables you to configure and create a database. Click Next.
5.	On the Database Templates window, select the type of database template to be used in creating the database. You can click Show Details to see the configuration for each type of database. Choose the template suited to the type of workload your database will support. If you are not sure, select the default General Purpose or Transaction Processing template. Click Next.
6.	On the Database Identification window, enter a Global Database Name and SID. Click Next. Note: If you created a database as part of your installation of the Oracle software and you are creating a second database with DBCA, you must choose a different global database name and SID for your second database.
7.	The Management Options window appears. To use Enterprise Manager, select Configure Enterprise Manager. Select Configure Database Control for local management to manage your database locally as appropriate to your configuration. Click Next.
8.	On the Database Credentials window, you can choose to use different administrative passwords or use the same password for all accounts. Select one of the options and enter your password data. ClickNext.
9.	For storage options, select File System, Automatic Storage Management, or Raw Devices as appropriate to your environment. Click Next.
10.	Select Specify Flash Recovery Area and enter a directory location and size. You may also choose to Enable Archiving to place your database in ARCHIVELOG mode. Click Next.
11.	Select Sample Schemas if you want to include the Sample Schemas (EXAMPLE) tablespace in your database. Click Next.
12.	The Memory window appears. Select Typical and enter a Memory Size (SGA and PGA). Click theSizing tab.
13.	The Sizing window appears. Specify the smallest block size and the maximum number of operating system user processes that can simultaneously connect to the database. Note: You cannot specify the block size if you are using a template. Click the Character Sets tab.
14.	The Character Sets window appears. Select the character set for your database. Click theConnection Mode tab.
15.	The Connection Mode window appears. Select Dedicated Server Mode or Shared Server Modeas appropriate for your environment. Click Next.
16.	On the Database Storage window, you can specify storage parameters for the database creation. Accept the default values. Click Next.
17.	On the Creation Options window, select Create Database to create your database. You can also select Save as a Database Template to save your configuration. Click Finish.
18.	At the Confirmation window, confirm the options that will be installed and click OK.
19.	Your database is now being created. After the database is created, you can change or unlock your passwords or click Exit.

Summary

In this tutorial, you learned how to:

1)	Install the basic version of the database.
2)	Install the advanced version of the database including running the Database Configuration Assistant.
3)	Create a database using the Database Configuration Assist