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 ….

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