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I have a Linux program which can write information to stdout and stderr.

I have a shell script which redirects that output to a file in /var/log. (Via >> and 2>&1.)

Is there a way to make that log file rotate? (max size, then switch to a different file, keep only a limited number of files)

I've seen a few answers which talk about the logrotate program, which sounds good, but they also seem to be focused on programs which are generating log files internally and handle HUP signals. Is there a way to make this work with a basic output redirection script?

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Why can't you just modify the script that redirects the output to contain the logic for the rotation? – MaQleod Jun 1 '11 at 5:05
I could, if someone could tell me how to detect the size of a logfile and rotate it out from under the stdout of a process without disturbing that process. I don't have to use logrotate if there's a better option, that just sounded like a convenient starting point for discussion. – Miral Jun 1 '11 at 5:12
You don't have to use logrotate, but using logrotate just saves time... There is usually little point reinventing the wheel. – bubu Jun 1 '11 at 5:43
Exactly my point. So is there a way to make logrotate work with an ongoing process's redirected stdout? – Miral Jun 1 '11 at 6:12

3 Answers

up vote 5 down vote accepted

As an alternative, you could pipe the output through tools designed with the primary purpose of maintaining size-capped, automatically rotated, log file sets, such as:

Tools to then process multilog-format log file sets include, amongst others:

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Thanks, multilog looks like just what I needed. – Miral Jun 3 '11 at 1:36
up vote 6 down vote

If you can have it go to one of the standard log streams (syslog, daemon, cron, user, security, mail, etc.) you can use the logger command and pipe to it instead.

echo "Hello." | logger -p daemon.info

Otherwise, you may be better off piping your logged content to a custom program or script to handle it, or look at setting up the logrotate configuration.

EDIT: JdeBP's answer seems to have what you may be looking for.

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+1 for simplicity. BTW, you can also configure a custom facility (local0) instead of the standard ones (daemon in your example) – Roger Keays Oct 9 '12 at 7:56
up vote 4 down vote

the rotatelogs tool shipped with apache (in the bin dir) (see docs) takes input from stdin and rotates the log after some specific amount of time

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