topic Re: log rotation by command > in Operating System - HP-UX

log rotation by command >

Shivkumar — Tue, 16 Aug 2005 04:37:26 GMT

Why most of the log files gets rotated using the command "> logfilename" ?

Thanks,
Shiv

Re: log rotation by command >

Peter Godron — Tue, 16 Aug 2005 04:39:53 GMT

Shiv,
the > logfilename is a redirect of output command.
Please clarify your question.

Re: log rotation by command >

Joseph Loo — Tue, 16 Aug 2005 04:41:11 GMT

hi,

that do not rotate the log file (or any file for that matter). it will "null" or empty the file, i.e. create a zero-length file.

# man null
for more info.

regards.

Re: log rotation by command >

Vibhor Kumar Agarwal — Tue, 16 Aug 2005 04:46:46 GMT

I think he is talking about using the same name of logfiles after sometimes.

Well,
With time logfiles become very large in size and slowly they can occupy your whole filesystem.

So its a good convention after sometime you start using the same logfile.

Re: log rotation by command >

Leif Halvarsson_2 — Tue, 16 Aug 2005 05:06:11 GMT

Hi,
"> logfilename" is truncating, not rotating (all previous information is lost).

Some logfiles is "rotated" (old file renamed and a new created) automatic at reboot or login (e.g. the syslog.log or the $HOME/.dt/startlog).

Re: log rotation by command >

Victor BERRIDGE — Tue, 16 Aug 2005 05:11:31 GMT

Hi,
Do not get confused as Leif mentionned > will overwrite what was there previously to append to you would need >>

Now as for rotating logs you would use your own custum scripts or tool like logrotate:
http://hpux.connect.org.uk/hppd/hpux/Sysadmin/logrotate-2.5/

All the best
Victor

Re: log rotation by command >

Simon Hargrave — Tue, 16 Aug 2005 05:11:45 GMT

The full procedure to "rotate" a logfile is something like: -

cp /var/adm/syslog/syslog.log /var/adm/syslog/syslog.log.`date +%d%m%y`
> /var/adm/syslog/syslog.log

This copies the contents of the file to a dated file then empties the existing log. You would probably also compress the dated log.

The reason you can't just move the file is that because the file is open (by the syslog daemon in this case), the file even though renamed still gets written to.

A process when opening a file attaches to the inode (underlying pointer), so when you rename a file the inode remains the same.

Re: log rotation by command >

Vibhor Kumar Agarwal — Tue, 16 Aug 2005 05:19:14 GMT

I don't think this will works.

I have a file open for writing then simply doing a cat terminates that process.

Here you truncating the whole file which is still open.

Re: log rotation by command >

Devender Khatana — Tue, 16 Aug 2005 07:55:14 GMT

Hi,

--->I have a file open for writing then simply doing a cat terminates that process.

Not in every case. Sometimes even when you remove the file , the process will keep on. Also it will not release the blocks occupied by such file and the process needs to be terminated manually if you need to get the free space.

>logfilename works for any file you need to null out and not only for the logfiles. This redirects the null to the content of the file, inturn making it a zero byte file.

The samething will be achived by 0>filename.

HTH,
Devender