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For my latest project, Auto Swatch, I needed a process management system to handle the availability of critical services, like nginx, memcached, PostgreSQL, and the application's Gunicorn processes. We use Supervisor at Dwaiter, so this was my natural choice.
"Supervisor is a client/server system that allows its users to monitor and control a number of processes on UNIX-like operating systems."
Steve Losh said that the trick to getting anything working with Supervisor is to make sure it doesn't daemonize. But, alas, there are other tricks.
This blog post concerns getting PostgreSQL working with Supervisor.
First, install PostgreSQL normally. On Ubuntu 10.10, the default way of
running PostgreSQL is via Unix socket. This socket lives at
/var/run/postgresql. Now, believe it or not, this creates a problem
when trying to run PostgreSQL in foreground mode, as required by
Supervisor. More on that later.
To understand the problem, you have to understand how PostgreSQL runs
normally. Typically, you run PostgreSQL via init script, like
/etc/init.d/postgresql start. This script runs a bunch of code, some
of which actually creates the dir
/var/run/postgresql and sets the
Problem: when you run PostgreSQL in foreground mode with Supervisor, it
tries to open the socket in
/var/run/postgresql. This will work if
you've previously run PostgreSQL with the init script, because the init
script created and set the permissions for that dir. However, after
reboot, that dir will be gone, and PostgreSQL won't be able to open the
socket there, resulting in failure. So, we either need to move the
socket (meaning a config change with your app), or make PostgreSQL run
on a TCP port instead. TCP port it is.
To get things running with Supervisor:
- Stop PostgreSQL:
sudo /etc/init.d/postgresql stop
- Move the init script somewhere safe:
sudo mv /etc/init.d/postgresql ~/somewhere-safe(so it won't startup in daemon mode)
- Edit the PostgreSQL config:
sudo vim /etc/postgresql/8.4/main/postgresql.conf
- Line 49: comment out
external_pid_file(not needed for TCP mode)
- Line 63: comment out port (unless you want to change the default port of 5432)
- Line 68: change
With this config, PostgreSQL will default to using TCP port 5432 instead of a Unix socket.
Here's what my Supervisor conf looks like for PostgreSQL:
[program:postgresql] user=postgres command=/usr/lib/postgresql/8.4/bin/postmaster -D "/var/lib/postgresql/8.4/main" process_name=%(program_name)s stopsignal=INT autostart=true autorestart=true redirect_stderr=true `
Now, you might also get an error about PostgreSQL not being able to read
the config file at
I had to symlink:
sudo ln -s /etc/postgresql/8.4/main/postgresql.conf /var/lib/postgresql/8.4/main/postgresql.conf
Your mileage may vary. Good luck.