Unix Ground

2011-06-14T14:45:00.001+05:30

Tag cloud taken from http://www.wordle.net/

Bourne shell redirection

2010-06-09T08:18:00.003+05:30

0 is stdin;
1 is stdout;
2 is stderr

redirect std err to file
$command 2>file

direct the output from command to stderr
$commamd >& 2

direct std output and std err to a file or /dev/null
$ command >file.log >>file.log
$ command >file.log 2>&1
$ command >/dev/null 2>&1

Some cool one liners..

2010-06-09T08:12:00.003+05:30

sum numbers in first column of a file
$ cat filename | awk 'BEGIN { tot=0 } { tot+=$1 } END { print tot }'

only print certain lines in a file, eq 20 - 30
$ sed -n -e 20,30p filename

Search all files in and below for a string xyz:
$ find . -exec egrep xyz {} \; -print

Remove all files name ".log.tmp"
$ find . -name .log.tmp -exec rm {} \;

search a file for any of three strings:
$ egrep 'abc|xyz|or' filename

Sexy Unix Commands

2010-01-20T13:47:00.006+05:30

the follwing are the sexy commands.
date;
unzip;
touch;
strip;
finger;
mount;
gasp;
yes;
uptime;

removing duplicate files using shell script

2009-05-06T19:17:00.002+05:30

Friends,

One liner script provided below, can be used to identify the duplicate files within the system. If you want to search in a partticular path, just replace it with "/tmp" provided in sample command. It will redirect all the duplicate file names into removal_list.txt which can be used to delete them.

find /tmp "$@" -type f -print0 xargs -0 -n1 md5sum sort --key=1,32 uniq -w 32 -d --all-repeated=separate sed -r 's/^[0-9a-f]*( )*//;s/([^a-zA-Z0-9./_-])/\\\1/g;s/(.+)/#rm \1/' >> removal_list.txt

Performance comparision

2009-05-06T19:16:00.002+05:30

Checkout the "time" command.

For checking the time taken for execution of any command do the following:

Say you want to execute "ls -l grep sanju.txt" and measure time taken for this.
Now open a bash shell and on the prompt
$time ls -l grep sanju.txt

it shows you the time taken by the command execution

Unaliasing in BASH

2009-05-05T16:46:00.000+05:30

Unaliasing in BASH
How can we unalias a command temporarily without using unalias command ?

just put the escape character before the command i.e. "\"e.g. :-

$\ls

It will show the without alias.

How to count a particular word in VI?

2009-01-22T09:42:00.001+05:30

If you want to count a particular word, say PROG, in a file, try this trick

:1,$s/zebra/&/g

or

if you want to count all words in a file, try

g [ctrl-g] at command mode

source: http://www.vim.org/tips/tip.php?tip_id=689

Some useful commands

2009-01-22T09:38:00.002+05:30

df : report disk free space
gview : load VIM, improved vi editor
history : display a list of previous commands
!! : repeat previous command
ls -p grep "/" : list sub-directories in the current directory
touch file.ext : create a NULL file named 'file.ext'
vmstat : virtual memory status
uname : system information

How to kill a hanged/freezed application ?

2009-01-22T09:33:00.002+05:30

Have you ever faced a hanged/freezed application while working at GUI of linux/sun etc?
If yes, this topic is for YOU.

Xkill is a utility for forcing the X server to close connections to clients. This program is very dangerous, but is useful for aborting programs that have displayed undesired windows on a user's screen. If no resource identifier is given with -id, xkill will display a special cursor as a prompt for the user to select a window to be killed.

We can use 'xkill' for a hard-to-kill frozen application. First, open a new terminal and type "xkill". After this your cursor will be a square-shaped.

Move to frozen findow and click.

TRIMMING THE LOG

2008-09-17T10:19:00.002+05:30

Various unix processes canproduce fast growing logs thatsometimes need to be trimmedinstead of deleted, for referenceor troubleshooting. And youlikely have no desire to edit thefiles. Here is a handy kshscript that will quickly trimthe log so it keeps recentinformation and lets you keep asmany lines as you think you mightneed.

I call it trimlog:

#! /bin/sh
# trimlog
filesize=`cat $1wc -l`
trim=`expr $filesize - $2`
if [ $trim -gt 0 ]
then
sed "1,$trim d" $1 > /tmp/$1
mv /tmp/$1 $1
echo $1 trimmed by $trim lines
else
echo "Invalid argument"
fi
Use it by feeding in the name of the log you want to trim followedby the number of lines you want to keep:

# trimlog oracle_listener.log 10000

Of course you can't use it in the /tmp directory.
There are probably newer and more efficient ways to do this, but this works.

kill really does not KILL

2008-09-17T10:14:00.002+05:30

kill is not really meant only to kill a process. But mainintention is to send a signalto process. And the processhandles these signals to dovarious tasks.

kill -INT 1234

where 1234 is the Process ID is really, this set an interrupt signal, Ctrl-C is an example of interupt signal givento shell.

kill -HUP 1234

some UNIX daemons handle this, to do refreshing business.

kill -KILL 1234

This is the sure kill,which cannot be handled by any process. Also know as,

kill -9 1234

Just, check the in the file /usr/include/sys/signal.h for all signals on the system or you can use:

kill -l

to get the complete list of signals.

Note: More about this can be found onkill and signal man pages.

AUTOMATIC LOGIN TO REMOTE HOSTS w/o PASSWORD

2008-09-17T10:11:00.001+05:30

Consider two hosts.host1.domain.comhost2.domain.com

>From hosts (user:deepak), you wish to logon tohost1 (user:paul).

Paul would create a .rhostsfile in his directory

chmod 744 .rhosts

(No write permission forothers)
The first line would contain

host1.domain.com deepak

Now, deepak should be able to logon to host2.domain.comas user paul by using rlogin.
Deepak will type

e.g.
rlogin hosts.domain.com -l paul

And he should be in.

ELIMINATING MULTIPLE SPACES

2008-09-17T10:09:00.001+05:30

Here is a simple script whichhelps in eliminating multiplespaces when one wants toextract a particular columnin a set of records from afile.

Here is an example to provethe same:

ps -u $LOGNAME tr -s " " : cut -d: -f

The above script line can beused to extract a column fromthe output of a ps command for a particular user ($LOGNAME).

CRYPT AN ASCII FILE

2008-09-15T15:53:00.002+05:30

An ascii file can be easily encrypted and decrypted.
To encrypt simply pipe the STDOUT ofthe file to "crypt" and redirect it toa new file name. Enter a passowrd whenprompted with "Enter key".

$ cat foo crypt > foo.e
Enter key:

To unencrypt simply pipe the STDOUT ofthe encrypted file to "crpyt" andredirect it to a new file name. Entera passowrd when prompted with"Enter key".
$ cat foo.e crypt > foo.new
Enter key:

Getting access to your linux box without password

2008-09-04T12:44:00.003+05:30

For BSD:
In order to recover your root password, you must boot FreeBSD in single user mode, mount the filesystems read/write and issue the passwd command. The passwd command will not actually recover your root password, but will allow you to change it to something new.

Boot in single user mode
As the operating system is starting, it will display the following message:Hit [Enter] to boot immediately, or any other key for command prompt.
Booting [kernel] in 10 seconds...
You should now press the space bar, and you will see the following message:
Type '?' for a list of commands, or 'help' for more detailed help.ok>
Now type boot -s and press the enter key to start FreeBSD in single user mode.
ok> boot -s
After the system boots, you should see the statement:
Enter full pathname of shell or RETURN for /bin/sh:
Press the enter key and you will have a # prompt and you can change the password using passwod command

For RH Linux
Booting Single-User Mode
You may be able to boot single-user mode directly. If your system boots, but does not allow you to log in when it has completed booting, try single-user mode.
If you are using GRUB, use the following steps to boot into single-user mode:
If you have a GRUB password configured, type p and enter the password.
Select Red Hat Linux with the version of the kernel that you wish to boot and type e for edit. You will be presented with a list of items in the configuration file for the title you just selected.
Select the line that starts with kernel and type e to edit the line.
Go to the end of the line and type single as a separate word (press the [Spacebar] and then type single). Press [Enter] to exit edit mode.
Back at the GRUB screen, type b to boot into single user mode.
After boot, you can change the password of root using passwd command

CASE TRANSLATION

2008-09-04T12:39:00.002+05:30

If you have occasion whereyou need to translate uppercase to lower and viceversa, and happen to run aksh, enter the following functions into your .bash_profile:

trans ()
{
tr '[:upper:]' '[:lower:]' < $1 > $2
}
TRANS()
{
tr '[:lower:]' '[:upper:]' <$1 > $2
}
The first function trans will translate all uppercaseletters in the first file(argument) to lowercase in the second file.
The second function TRANS does the exact opposite.

Tip within unix

2008-09-04T11:35:00.002+05:30

tip is a unix utility for establishing a terminal connection to a remote system via a modem

The tip command line options are as follows tip [-v] [-speed-entry] {hostname phone-number device}

A simple example is a script that establishes a terminal session:
spawn tip modem
expect "connected"
send "ATD$argc\r"
set timeout 30
expect "CONNECT"

Tracking User's activity using "script -a"

2008-08-01T12:42:00.004+05:30

Unix System provides a very good method allows us to capture of all commands issued by the user “XYZ”. For this, we can user "script" command. This will print all what appears on the screen (commands and their output) to the filename

But remember, Its not a User History.... It stores all commands entered by all users (.e. its the shell history .

Add the following line to your BASH profile

script -a ~/.termlog`date +%m%d%y`

This enable to capture all the terminal activities to a file ending with current date

Cut and paste text files by columns

2008-07-28T14:07:00.007+05:30

How many times have you wanted to edit those results files columnwise?

Here’s a generic UNIX way: (startcol and endcol refer to character columns, including whitespace. Tab counts as 1.)

cut -cstartcol-endcol file {>receiving file} paste sourcefile1 sourcefile2 {>final file}

I like to preview and fine-tune my commands by looking at the result on standard out (the shell window) and then redirecting output to a (temporary) file when things look right. Those feeling really adventurous can combine things into a single command line…

Great Unix Tips & Tricks: Vol 1

2008-07-28T14:07:00.005+05:30

Whether you are a newbie to Linux or you are a seasoned guru, you are bound to find some scripts or programs which just make your life on the computer exponentially easier. The following is a list of them and explains what they do.

1. tac

tac is a command similar to cat, except that it reverses the output of the specified file.

tac

2. Multiple X-Sessions

Using multiple X-Sessions allows a user to have open more than just one instance of XFree, so multiple desktop environments can be used at a time.

startx -- :

terminal name is simply which terminal X should start on. By default it starts on

0:0. If you want two open, you may want it open on 0:1, which can be run by:

startx -- :1

The resulting desktops will exist on F7 - F12.

3. links

links is a text based browser which has full support for tables

links

is simply the hostname or IP address of the computer to connect to.

sparse files

2008-07-28T14:07:00.001+05:30

Due to the Unix concept of sparse files, you can create seemingly enormous files that in reality take next to no disk space. The following program will create a 305,419,897 byte file called 'core' that may result in you receiving a 'cleanup' email message from a less-than-seasoned Unix sysadmin even though it occupies virtually no real disk space.

    $ cat bigcore.c
    #include 
    #include 

    int main(void) {
        int fd = open("core", O_CREAT|O_WRONLY|O_TRUNC, 0600);
        lseek(fd, 0x12345678, SEEK_SET);
        write(fd, "1", 1);
        close(fd);
        return 0;
    }

    $ cc -o bigcore bigcore.c
    $ ./bigcore
    $ ls -l core
    -rw-------  1 dmr  staff  305419897 May  1 03:50 core
    $ du -k core
    48      core
    $

Ctrl+D or exit: Which one is better?

2008-07-15T14:44:00.003+05:30

In BASH, to exit from shell we can use Ctrl+D or exit ? which one is better?

-Ctrl+D conveniently exits Bash
-Sometimes too conveniently bcoz session may be terminated if pressed accidentaly.

To avoid the accidental exit, we can specify the no of "Ctrl+D" pressed before exit.

$export IGNOREEOF=1

$ Ctrl+D
$ Use "exit" to leave the shell.
$ Ctrl+D
$ exit

Games

2008-07-09T15:32:00.001+05:30

If you like to use Linux and only Linux, and you also like to play games on your computer, the best choice is to buy native Linux games (games that run without any intermediate layer on your Linux system). You can find lots of information about available games and even order them through the links below.

Naturally there are also lots of free games, many simple but fun games are included with Linux distributions, but some are not, so I have included links about those too.

Linux Game Publishing
Tux Games
Linux Gaming
Linuxgames
The Linux Game
Mandrake eXPerience FREE GAMES section
Article on Gaming and Linux in 2003

Command based Calculator in BASH

2008-07-08T16:24:00.002+05:30

Bash can perform simple arithmetic operations at the command prompt.

To use this feature, simply type in the arithmetic expression you wish to evaluate at the prompt within double parentheses, as illustrated below. Bash will attempt to perform the calculation and return the answer.

bash> echo $((16/2))
8

bash> echo $((16*2))
32