Shell Scripting - referrence

-nt : Newer than
-ot : Older than
-gt : Greater than
-lt : Less than
-ge : Greater than or equal to
-le : less than or equal to 
-eq : equal to 
-ne : not equal to 

check if the name "abc" is file or not
test -f abc; echo $? - if o/p is 0 then its a file else its a directory

also, 
[-f abc]; echo $?

to check socket files eg mysql.sock
test -S /var/lib/mysql/mysql.sock; echo $? - if o/p is 0 then its socket file else not

To check null (zero size) files
test -s log1.log; echo $? - if o/p is 0 then its not a zero byte file.

man test - for all details 

NTP Server restart

/etc/init.d/ntp start
/etc/init.d/ntp stop
/etc/init.d/ntp restart 

Different ways of identifying whoe is logged on linux server

$ w
23:04:27 up 29 days,  7:51,  3 users,  load average: 0.04, 0.06, 0.02
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
ramesh   pts/0    dev-db-server        22:57    8.00s  0.05s  0.01s sshd: ramesh [priv]
jason    pts/1    dev-db-server        23:01    2:53   0.01s  0.01s -bash
john     pts/2    dev-db-server        23:04    0.00s  0.00s  0.00s w

$ w -h
ramesh   pts/0    dev-db-server        22:57   17:43   2.52s  0.01s sshd: ramesh [priv]
jason    pts/1    dev-db-server        23:01   20:28   0.01s  0.01s -bash
john     pts/2    dev-db-server        23:04    0.00s  0.03s  0.00s w -h

$ w -u 23:22:06 up 29 days,  8:08,  3 users,  load average: 0.00, 0.00, 0.00
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
ramesh   pts/0    dev-db-server        22:57   17:47   2.52s  2.49s top
jason    pts/1    dev-db-server        23:01   20:32   0.01s  0.01s -bash
john     pts/2    dev-db-server        23:04    0.00s  0.03s  0.00s w -u

$ w -s
23:22:10 up 29 days,  8:08,  3 users,  load average: 0.00, 0.00, 0.00
USER     TTY      FROM               IDLE WHAT
ramesh   pts/0    dev-db-server        17:51  sshd: ramesh [priv]
jason    pts/1    dev-db-server        20:36  -bash
john     pts/2    dev-db-server         1.00s w -s

2. Get the user name and process of logged in user using who and users command
who command
 is used to get the list of the usernames who are currently logged in. 
Output of the who command contains the following columns: user name, tty
 number, date and time, machine address.

 
$ who
ramesh pts/0        2009-03-28 22:57 (dev-db-server)
jason  pts/1        2009-03-28 23:01 (dev-db-server)
john   pts/2        2009-03-28 23:04 (dev-db-server)
 
To get a list of all usernames that are currently logged in, use the following:

 
$ who | cut -d’ ‘ -f1 | sort | uniq
john
jason
ramesh
 

 

Users Command
users command
 is used to print the user name who are all currently logged in the 
current host. It is one of the command don’t have any option other than 
help and version. If the user using, ‘n’ number of terminals, the user 
name will shown in ‘n’ number of time in the output.

 
$ users
john jason ramesh

3. Get the username you are currently logged in using whoami
whoami command is used to print the loggedin user name.

 
$ whoami
john
 
whoami command gives the same output as id -un as shown below:

 
$ id -un
john
 
who am i
 command will display the logged-in user name and current tty details. 
The output of this command contains the following columns: logged-in 
user name, tty name, current time with date and ip-address from where 
this users initiated the connection.

 
$ who am i
john     pts/2        2009-03-28 23:04 (dev-db-server)

$ who mom likes
john     pts/2        2009-03-28 23:04 (dev-db-server)

Warning: Don’t try “who mom hates” command.
Also, if you do su to some other user, this command will give the information about the logged in user name details.

 

4. Get the user login history at any time
last command
 will give login history for a specific username. If we don’t give any 
argument for this command, it will list login history for all users. By 
default this information will read from /var/log/wtmp file. The output 
of this command contains the following columns:

 

User name
Tty device number
Login date and time
Logout time
Total working time

$ last jason
jason   pts/0        dev-db-server   Fri Mar 27 22:57   still logged in
jason   pts/0        dev-db-server   Fri Mar 27 22:09 - 22:54  (00:45)
jason   pts/0        dev-db-server   Wed Mar 25 19:58 - 22:26  (02:28)
jason   pts/1        dev-db-server   Mon Mar 16 20:10 - 21:44  (01:33)
jason   pts/0        192.168.201.11  Fri Mar 13 08:35 - 16:46  (08:11)
jason   pts/1        192.168.201.12  Thu Mar 12 09:03 - 09:19  (00:15)
jason   pts/0        dev-db-server   Wed Mar 11 20:11 - 20:50  (00:39

Clone Permission

List all the files with ownership and full path :

find $PWD -type d  -ls

List all the directories with ownership and full path :

find $PWD -type f  -ls

List all the permissions with full path recursively :

find ${PWD} -exec stat -c' %a %n' {} \;

 ==================================================================

Script to Change Files

Usage : this script and file name

Script.sh filename

#! /bin/bash

i=0

t=`cat $1 | wc -l`

while [ $i -lt $t ]

        do

                i=$[$i + 1]

                read line

                user=`echo $line | awk '{print $5}'`

                group=`echo $line | awk '{print $6}'`

                file=`echo $line | awk '{print $NF}'`

                #echo $user

                #echo $group

                #echo $file

                chown $user:$group $file

                if [ $? -eq 0 ] ; then

                        echo File  $line is updated >> /tmp/updatedFiles.txt

                        else

                        echo File $line is failed >> /tmp/updatedFilesFailed.txt

                fi

        done < $1

#END

==================================================================

Script to ChangeDir

Usage : this script and file name

Script.sh filename

#! /bin/bash

i=0

t=`cat $1 | wc -l`

while [ $i -lt $t ]

        do

                i=$[$i + 1]

                read line

                user=`echo $line | awk '{print $5}'`

                group=`echo $line | awk '{print $6}'`

                file=`echo $line | awk '{print $NF}'`

#               echo $user

#               echo $group

#               echo $file

                chown $user:$group $file

                if [ $? -eq 0 ] ; then

                        echo Directory  $line is updated >> /tmp/updatedDirs.txt

                        else

                        echo Directory $line is failed >> /tmp/updatedDirsFailed.txt

                fi

        done < $1

#END

==================================================================

Changes permission for all the files :

Script to Change Files

Usage : this script and file name

Script.sh filename

#! /bin/bash

i=0

t=`cat $1 | wc -l`

while [ $i -lt $t ]

        do

                i=$[$i + 1]

                read line

                permission=`echo $line | awk '{print $1}'`

                file=`echo $line | awk '{print $NF}'`

                #echo $permission

                #echo $file

                chmod $permission $file

                if [ $? -eq 0 ] ; then

                        echo Permission  $line is updated >> /tmp/updatedPermission.txt

                        else

                        echo Permission $line is failed >> /tmp/updatedPermissionFailed.txt

                fi

        done < $1

#END