I assume you are unable to simply extend the filesystem in question (using
lvextend && ext2online), because you do not use LVM or use wrong filesystem type.
What you've proposed might work if you signal the daemons with SIGHUP (kill -1 pid). Obviously you would need to later on "mount -o bind / /somewhere" and clean up what has been left underneath mounted /var/log. But it has a bad smell for me, especially for production.
Avoid downtime, have a clean result (but complicated to do)
Forget about "mount -o bind" idea, create a new LV/partition, but don't mount it yet.
lsof | grep /var/log # lists open files in /var/log
For each daemon that has any open file (I would expect at least syslog, inetd, sshd):
- reconfigure the daemon no to log to /var/log
- refresh the daemon (
kill -1 or
- confirm with
lsof | grep /var/log that daemon has closed its files
Mount over /var/log.
Restore old configurations, SIGHUP/reload daemons again.
Easy way (downtime)
Create a new LV/partition and mount it properly over either /var or /var/log. The easy way is to take down the server to maintenance mode (single-user mode), and use the actual console (not ssh) for the operation.