Do it with logrotate, just tell it what you want...
rotate 7305 # 2 decades
create 644 nginx root
if [ -f /var/run/nginx.pid ]; then
kill -USR1 `cat /var/run/nginx.pid`
I don't use nginx, so I used an example I found for the postrotate... If you have a logrotate script already, start with modifying that.
- "daily" means every day. You could do weekly or size-based, but that doesn't interact as prettily with "dateext".
- "dateext" means it'll give the rotated logfiles a name based on the date instead of a simple number; that way it doesn't have to rename every log file every day and you can tell the date of a logfile from the name of the file
- "rotate 7305" -- this is two decades. Keep more or less... logrotate really prefers to have some sort of retirement, but you can set it ridiculously high.
- "olddir" has to be on the same filesystem, but that'll keep the logs in a separate dir so you can figure out what's going on
- "delaycompress" and "create" help make sure it works with software that doesn't want to work with it