== Unix and Linux Tips for day to day trouble shooting ==
**To know your Linux Distro and the Version
more /etc/redhat-release
**memory information
free -m
**Command to get the files based on size (Unit is blocks )
find . -size +10000 -exec ls -l {} \;
**To find paTterns in Files
find . -name "log_200812*" -exec grep FS8LM {} \; -print
**remote connecting to another machine and executing a command using telnet.
(sleep 3; echo username; sleep 3; echo password; sleep 5; echo "ls -l"; sleep 3; echo "exit") | telnet hostname
**tar- the archive utility
tar tvf filename.tar --- View the table of content of a tar archive
tar xvf filename.tar --- Extract content of a tar archive
tar cvf filename.tar file1 file2 file3 --- Create a tar archive called filename.tar using file1, file2,file3 .
tar can't copy the special files , device files .Not suitable for taking root backup.
**VI editor - Find and replace
To find & replace all occurances of a particular text string, use the command:
:%s/text1/text2/g[RETURN]
which replaces all occurances of text1 with text2.
**Advanced GREP
To display all lines in the file1 file that match either the abc or xyz string, enter: grep -E "abc|xyz" file1
**the cut tab delimiter technique to extract each field when doing an ls -l command
ls -la |tr -s ' '|cut -d' ' -f5,8
**list all open files
lsof
**list down the FolderSize of all the folders inside the current folder
du -h -c --max-depth=1 2>/dev/null
**finding files more than a particularr size
find . -size +100000k -mtime +60 -exec ls -al '{}' \;
**Tell how long the system has been running and list thee load average value.
uptime
e.g
diham@diham] uptime
19:48:11 up 9 days, 19:56, 2 users, load average: 0.00, 0.00, 0.00
**Copying file to host:
scp SourceFile user@host:directory/TargetFile
**Copying file from host:
scp user@host:directory/SourceFile TargetFile
**The Crontab : Master of UNIX scheduling
crontab -e -> edit the crontab
crontab -l -> list the crontab entries
crontab -r -> remove the cron file
crontab -v -> last edited time of cron file
The entries in the file are
* * * * * command
minute hour dayofmonth month week command
e.g
0,15,30,45 * * * * /home/user/mycommand1 --> runs the mycommand1 every 15 mins
** '''Run Level Commands'''
The init process is the last step in the boot procedure and identified by process id "1". Init is responsible for starting system processes as defined in the /etc/inittab file.The init process is never shut down. It is a user process and not a kernel system process although it does run as root.
* Shutdown:
o init 0
o shutdown -h now
+ -a: Use file /etc/shutdown.allow
+ -c: Cancel scheduled shutdown.
o halt -p
+ -p: Turn power off after shutdown.
o poweroff
* Reboot:
o init 6
o shutdown -r now
o reboot
* Enter single user mode:
o init 1
** ldconfig
ldconfig - Updates the Symbolic links in /usr/lib , /lib and and directories mentioned in the file /etc/ld.so.conf
**Unpacking RPM
rpm2cpio libstdc++-4.3.2-7.i386.rpm|cpio -i --make-directories
**To know your Linux Distro and the Version
more /etc/redhat-release
**memory information
free -m
**Command to get the files based on size (Unit is blocks )
find . -size +10000 -exec ls -l {} \;
**To find paTterns in Files
find . -name "log_200812*" -exec grep FS8LM {} \; -print
**remote connecting to another machine and executing a command using telnet.
(sleep 3; echo username; sleep 3; echo password; sleep 5; echo "ls -l"; sleep 3; echo "exit") | telnet hostname
**tar- the archive utility
tar tvf filename.tar --- View the table of content of a tar archive
tar xvf filename.tar --- Extract content of a tar archive
tar cvf filename.tar file1 file2 file3 --- Create a tar archive called filename.tar using file1, file2,file3 .
tar can't copy the special files , device files .Not suitable for taking root backup.
**VI editor - Find and replace
To find & replace all occurances of a particular text string, use the command:
:%s/text1/text2/g[RETURN]
which replaces all occurances of text1 with text2.
**Advanced GREP
To display all lines in the file1 file that match either the abc or xyz string, enter: grep -E "abc|xyz" file1
**the cut tab delimiter technique to extract each field when doing an ls -l command
ls -la |tr -s ' '|cut -d' ' -f5,8
**list all open files
lsof
**list down the FolderSize of all the folders inside the current folder
du -h -c --max-depth=1 2>/dev/null
**finding files more than a particularr size
find . -size +100000k -mtime +60 -exec ls -al '{}' \;
**Tell how long the system has been running and list thee load average value.
uptime
e.g
diham@diham] uptime
19:48:11 up 9 days, 19:56, 2 users, load average: 0.00, 0.00, 0.00
**Copying file to host:
scp SourceFile user@host:directory/TargetFile
**Copying file from host:
scp user@host:directory/SourceFile TargetFile
**The Crontab : Master of UNIX scheduling
crontab -e -> edit the crontab
crontab -l -> list the crontab entries
crontab -r -> remove the cron file
crontab -v -> last edited time of cron file
The entries in the file are
* * * * * command
minute hour dayofmonth month week command
e.g
0,15,30,45 * * * * /home/user/mycommand1 --> runs the mycommand1 every 15 mins
** '''Run Level Commands'''
The init process is the last step in the boot procedure and identified by process id "1". Init is responsible for starting system processes as defined in the /etc/inittab file.The init process is never shut down. It is a user process and not a kernel system process although it does run as root.
* Shutdown:
o init 0
o shutdown -h now
+ -a: Use file /etc/shutdown.allow
+ -c: Cancel scheduled shutdown.
o halt -p
+ -p: Turn power off after shutdown.
o poweroff
* Reboot:
o init 6
o shutdown -r now
o reboot
* Enter single user mode:
o init 1
** ldconfig
ldconfig - Updates the Symbolic links in /usr/lib , /lib and and directories mentioned in the file /etc/ld.so.conf
**Unpacking RPM
rpm2cpio libstdc++-4.3.2-7.i386.rpm|cpio -i --make-directories
