Proper design
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.
Your approach
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 /etc/init.d/script reload)
- 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.
Best Answer
This article discusses configuring log rotation limits (see management studio express). According to the definition of the error log, it does not seem to be essential for your instance to run properly. I would say it is safe to delete, but you likely want to configure rotation.