log rotation by command >

[Shivkumar]

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

Thanks,
Shiv

[Peter Godron]

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

[Joseph Loo]

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.

[Vibhor Kumar Agarwal]

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.

[Leif Halvarsson_2 · Accepted solution]

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).

[Victor BERRIDGE]

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

[Simon Hargrave]

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.

[Vibhor Kumar Agarwal]

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.

[Devender Khatana]

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