Troubleshooting Varnish

Sometimes Varnish misbehaves. In order for you to understand whats going on there are a couple of places you can check. varnishlog, /var/log/syslog, /var/log/messages are all places where varnish might leave clues of whats going on.

When Varnish won't start

Sometimes Varnish wont start. There is a plethora of reasons why Varnish wont start on your machine. We've seen everything from wrong permissions on /dev/null to other processes blocking the ports.

Starting Varnish in debug mode to see what is going on.

Try to start varnish by:

# varnishd -f /usr/local/etc/varnish/default.vcl -s malloc,1G -T  -a -d

Notice the -d option. It will give you some more information on what is going on. Let us see how Varnish will react to something else listening on its port.:

# varnishd -n foo -f /usr/local/etc/varnish/default.vcl -s malloc,1G -T  -a -d
storage_malloc: max size 1024 MB.
Using old SHMFILE
Platform: Linux,2.6.32-21-generic,i686,-smalloc,-hcritbit
200 193
Varnish Cache CLI.
Type 'help' for command list.
Type 'quit' to close CLI session.
Type 'start' to launch worker process.

Now Varnish is running. Only the master process is running, in debug mode the cache does not start. Now you're on the console. You can instruct the master process to start the cache by issuing "start".:

bind(): Address already in use
300 22
Could not open sockets

And here we have our problem. Something else is bound to the HTTP port of Varnish. If this doesn't help try strace or truss or come find us on IRC.

Varnish is crashing

When varnish goes bust the child processes crashes. Usually the mother process will manage this by restarting the child process again. Any errors will be logged in syslog. It might look like this:

Mar  8 13:23:38 smoke varnishd[15670]: Child (15671) not responding to CLI, killing it.
Mar  8 13:23:43 smoke varnishd[15670]: last message repeated 2 times
Mar  8 13:23:43 smoke varnishd[15670]: Child (15671) died signal=3
Mar  8 13:23:43 smoke varnishd[15670]: Child cleanup complete
Mar  8 13:23:43 smoke varnishd[15670]: child (15697) Started

Specifically if you see the "Error in munmap" error on Linux you might want to increase the amount of maps available. Linux is limited to a maximum of 64k maps. Setting vm.max_map_count in sysctl.conf will enable you to increase this limit. You can inspect the number of maps your program is consuming by counting the lines in /proc/$PID/maps

This is a rather odd thing to document here - but hopefully Google will serve you this page if you ever encounter this error.

Varnish gives me Guru meditation

First find the relevant log entries in varnishlog. That will probably give you a clue. Since varnishlog logs so much data it might be hard to track the entries down. You can set varnishlog to log all your 503 errors by issuing the following command:

$ varnishlog -c -m TxStatus:503

If the error happened just a short time ago the transaction might still be in the shared memory log segment. To get varnishlog to process the whole shared memory log just add the -d option:

$ varnishlog -d -c -m TxStatus:503

Please see the varnishlog man page for elaborations on further filtering capabilities and explanation of the various options.

Varnish doesn't cache

See Achieving a high hitrate.

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