Linux Common Queries
Lot of readers asked me to post on Linux hence first post on Linux covers common queries from Apps DBA’s w.r.t. Linux.
If you use any command in Linux/Unix very frequently and wish to share with our readers please leave it as comment
Q: How 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)
Q: How 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 {} \;
Q: How 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
Q: How to find files changed in last N days (Solaris)
find <dir_name> -mtime -N -print
Q: How to extract cpio file
cpio -idmv < file_name (Don’t forget to use sign < before file name)
Q: How to find CPU & Memory detail of linux
cat /proc/cpuinfo (CPU)
cat /proc/meminfo (Memory)
Q: How 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
Q: How 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
Q: How 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)
Q: How 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 )
Q: How 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
Q: How 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)
Q: How 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 ftp, rman backup or removed old log files regularly.
More unix/linux commands coming soon ….