22

On Windows, you can set what should happen if/when a service fails. Is there a standard way of achieving the same thing on Linux (CentOS in particular)?

A bigger part of my question is: how do you handle sockets that have been left open - for example in TIME_WAIT, FIN_WAIT1, etc states.

At the moment if the service I am developing crashes, I have to wait for the sockets to clear or change the listen port before I can then manually restart it.

Thanks for your help.

26

monit is a great way to monitor and restart services when they fail--and you'll probably end up using this for other essential services (such as Apache). There's a nice article on nixCraft detailing how to use this for services specifically, although monit itself has many more functions beyond this.

As for the socket aspect, @galraen answered this spot on.

  • It's a shame I have to decide which is the answer. I should have asked two seperate questions. @gelraen your answer just ended my weeks of searching for a solution. Thanks you so much! @Redmumba thanks, Monit does look good! – Pryo Mar 26 '11 at 14:01
  • Whichever one you decide to mark correct, definitely upvote @gelraen's answer. Its spot on correct, and very informative. – Andrew M. Mar 26 '11 at 16:15
17

Only answering the service restart part. I came across Monit as well, but on CentOS 7 systemd takes care of all that for you. You just need to add these two lines to the .service file (if they're not there already):

Restart=always
RestartSec=3

See https://jonarcher.info/2015/08/ensure-systemd-services-restart-on-failure/ for reference.

If you want to create a custom systemd service, it's pretty straightforward to write your own service file. See the example below, for a custom http server.

Start the editor with a new service file:

vim /etc/systemd/system/httpd.service

And add the following content, which you can edit as required:

[Unit]
Description=My httpd Service
After=network.target

[Service]
Type=simple
User=root
Environment=PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
Environment=PERLLIB=/perl
ExecStart=/bin/httpd /etc/httpd.conf
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target

I want it to start automatically on boot:

systemctl enable httpd

Tell systemd about the changes and start the service:

systemctl daemon-reload
systemctl start httpd

And now you can see the status:

systemctl status httpd

For reference, see https://scottlinux.com/2014/12/08/how-to-create-a-systemd-service-in-linux-centos-7/

  • Yes, exactly, systemd, the standard service manager on most popular distributions, can do that for you. – Rolf Apr 8 at 12:53
13

You can call setsockopt(2) for listening socket with SO_REUSEADDR, so you will be able to bind(2) it again without waiting for expiring all connections. Another possibility: drop connections from kernel. FreeBSD have tcpdrop command for this, don't know about Linux.

4

If your linux distro uses Upstart instead of SysV init, then the respawn keyword does this.

http://upstart.ubuntu.com/cookbook/#respawn

  • Thanks, this looks like just the thing, but unfortunately I'm stuck with SysV init. – Pryo Mar 26 '11 at 14:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.