I know how to gracefully restart Apache web server under Unix like operating system. I made changes to nginx.conf. How do I gracefully restart Nginx web server? How do I make changes in a Nginx server config file to take effect without restarting the Nginx server itself without interrupting users’ current session?

From the nginx wiki pages

The master process can handle the following signals: TERM, INT Quick shutdown

• QUIT Graceful shutdown
• KILL Halts a stubborn process
• HUP Configuration reload. Start the new worker processes with a new configuration. Gracefully shutdown the old worker processes
• USR1 Reopen the log files
• USR2 Upgrade Executable on the fly
• WINCH Gracefully shutdown the worker processes

The syntax is as follows to

  kill -HUP $( cat /path/to/nginx.pid )

OR find nginx pid with the pgrep command or ps command:

pgrep nginx
ps aux | grep [n]ginx

Sample outputs:

root      4333  0.0  0.4  70776  9352 ?        Ss   Nov24   0:00 nginx: master process /usr/local/nginx/sbin/nginx
nginx     9921  1.0  0.5  70776  9888 ?        S    Dec05  19:24 nginx: worker process
nginx     9922  1.0  0.5  70776 10240 ?        S    Dec05  19:42 nginx: worker process
nginx     9923  0.0  0.4  70776  8724 ?        S    Dec05   0:00 nginx: cache manager process

Type the following command as root user:

kill -HUP 4333

If you are using Nginx version 0.7.53+
Pass the -s reload option:

# nginx -s reload

OR

# /usr/local/nginx/sbin -s reload

If you are using Debian / CentOS / RHEL / Fedora / Ubuntu Linux try

# /etc/init.d/nginx reload

If you are using FreeBSD try

# /usr/local/etc/rc.d/nginx reload

If you are using OpenBSD try

# /usr/sbin/nginx -s reload

OR

# /etc/rc.d/nginx reload

How do I reload / gracefully restart chrooted nginx server?
Type the following command:

/usr/sbin/chroot /jail /usr/local/nginx/sbin/nginx -s reload