Log Rotation

NGINX re-opens its logs in response to the USR1 signal.

Basic Rotation Script

mv access.log access.log.0
kill -USR1 `cat /var/run/nginx.pid`
sleep 1
gzip access.log.0  # or any other processing

Why sleep 1?

After sending USR1, NGINX needs a moment to finish writing to the old file descriptor before you can safely compress/process the old log.

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Logrotate Configuration

For systems using logrotate, create /etc/logrotate.d/nginx:

/var/log/nginx/*.log {
    daily
    missingok
    rotate 14
    compress
    delaycompress
    notifempty
    create 0640 www-data adm
    sharedscripts
    postrotate
        if [ -f /var/run/nginx.pid ]; then
            kill -USR1 `cat /var/run/nginx.pid`
        fi
    endscript
}

Directive	Purpose
daily	Rotate logs daily
rotate 14	Keep 14 days of logs
compress	Compress rotated logs with gzip
delaycompress	Delay compression by one rotation
sharedscripts	Run postrotate only once for all logs
postrotate	Send USR1 signal after rotation

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How It Works

1. The log file is moved/renamed
2. NGINX continues writing to the old file descriptor
3. USR1 signal tells NGINX to re-open log files
4. NGINX opens new log files with the original names
5. Old log files can now be safely processed

Access vs Error Logs

Both access_log and error_log are reopened on USR1.