Agree about the lock file to prevent race conditions.
I think you'll also run into problems when M reaches 10, because ls -1r won't sort numerically when the number of digits varies. You'd need to either stick to to single digits for the version number, or pipe the ls output to "sort -t. -k 3nr" to get a proper reverse numeric sort. Otherwise the rotation order will get really messed up.
On 12/07/2012 9:04 PM, Sean Walberg wrote:
I'd use a lock file just to be safe. Depending on how "restart-daemon" works you might end up with a race condition inside there, resulting in no daemon getting run until the next pass.
The easiest way would be
lock="/var/run/mylock" if [ -f $lock ]; then exit 1; else touch $lock; fi #do your magic rm $lock
There are other utilities like flock and lockfile if you are really concerned about re-entrancy, and depending on the user you run this script as, you may want to put $lock out of a normal user's reach. But to protect something running from cron, this will be more than enough.
Sean
On Thu, Jul 12, 2012 at 7:59 PM, Adam Thompson <athompso@dmts.biz mailto:athompso@dmts.biz> wrote:
I just wrote the following snippet to quickly rotate some log files. I know this runs without bound, that's acceptable and desirable in this case. What I'm worried about is creating race conditions if this gets run from cron every minute... ###check if daemon has died### if daemon-is-dead; then L=mydaemon.log shopt -u failglob for i in $( ls -1r ${L}.[0-9]* 2>/dev/null ); do N=${i#$L.} M=$(( ${N} + 1 )) mv -n $i "${L}.${M}" done if [ -f ${L} ] ; then mv -n ${L} ${L}.1; fi restart-daemon fi Am I shooting myself in the foot here? The obvious race condition is if two copies run simultaneously, but this is only for temporary debugging purposes. If necessary, I'll change the cron job from every minute to every five minutes. Even then, the '-n' option to GNU mv should protect me...? Does anyone have a safer way to do this sort of thing manually? I don't want this logfile managed by logrotate(8). -Adam Thompson DMTS (Contractor) athompso@dmts.biz <mailto:athompso@dmts.biz> (204) 291-7950 <tel:%28204%29%20291-7950> - direct (204) 489-6515 <tel:%28204%29%20489-6515> - fax _______________________________________________ Roundtable mailing list Roundtable@muug.mb.ca <mailto:Roundtable@muug.mb.ca> http://www.muug.mb.ca/mailman/listinfo/roundtable-- Sean Walberg <sean@ertw.com mailto:sean@ertw.com> http://ertw.com/
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