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Useful Linux Commands for DBA’s

Posted by appsinfo on January 27, 2010

As DBA you need to use frequent OS command, here I would like to share you some of the important day to day linux commands:

1. To delete files older than N number of days ? (Useful in delete log, trace, tmp file )
find . -name ‘*.*’ -mtime +[N in days] -exec rm {} \; ( This command will delete files older then N days in that directory, always good to use it when you are in applcsf/ tmp,out,log directory)

2. To list files modified in last N days
find . -mtime -<ndays> -exec ls -lt {} \;

So to find files modified in last 3 days
find . -mtime -3 -exec ls -lt {} \;

3. To sort files based on Size of file ? ( useful to find large files in log directory to delete in case disk is full )
ls -l | sort -nrk 5 | more

4. To find files changed in last N days (Solaris)
find <dir_name> -mtime -N -print

5. To extract cpio file
cpio -idmv < file_name
(Don’t forget to use sign < before file name)

6. To find CPU & Memory detail of linux
cat /proc/cpuinfo (CPU)
cat /proc/meminfo (Memory)

7. To find if Operating system in 32 bit or 64 bit ?
For solaris use command
isainfo -v
If you see out put like
32-bit sparc applications
That means your O.S. is only 32 bit
but if you see output like
64-bit sparcv9 applications
32-bit sparc applications
above means your o.s. is 64 bit & can support both 32 & 64 bit applications

8. To find if any service is listening on particular port or not ?
netstat -an | grep {port no}

For example if you know that OID is running on 389 port so to check if OID services is listening or not then use
netstat -an | grep 389

9. To find Process ID (PID) associated with any port ?
This command is useful if any service is running on a particular port (389, 1521..) and that is run away process which you wish to terminate using kill command
lsof | grep {port no.} (lsof should be installed and in path)

9. To change a particular pattern in a file ?
Open file using vi or any other editor, go in escape mode (by pressing escape) and use

:1,$s/old_pattern/new_parameter/gc ( g will change globally, c will ask for confirmation before changing )

10. To find a pattern in some file in a directory ?
grep pattern file_name
( to find pattern in particular file )
grep pattern * ( in all files in that directory )
If you know how to find a pattern in files in that directory recursively please answer that as comment

11. To create symbolic link to a file ?
ln -s pointing_to symbolic_name

e.g. If you want to create symbolic link from a -> b
ln -s b a
(Condition:you should have file b in that directory & there should not be any file with name a)

12. To setup cronjob (cronjob is used to schedule job in Unix at O.s. Level )
crontab -l( list current jobs in cron)
crontab -e ( edit current jobs in cron)

_1_ _2_ _3_ _4_ _5_ executable_or_job
Where
1 – Minutes (0-59)
2 – Hours ( 0-24)
3 – day of month ( 1- 31 )
4 – Month ( 1-12)
5 – A day of week ( 0- 6 ) 0 -> sunday 1-> monday

e.g. 0 3 * * 6 Means run job at 3AM every saturday

This is useful for scheduling tablespace threshold, ftp, rman backup or removed old log files, or other scripts regularly.

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