So your mongrels are humming along happily and you have monit monitoring them with a definition like this:
check process mongrel_8010 with pidfile /path/to/current/log/mongrel.8010.pid start program = "/usr/bin/mongrel_rails cluster::start -C /path/to/current/config/mongrel_cluster.yml --clean --only 8010" stop program = "/usr/bin/mongrel_rails cluster::stop -C /path/to/current/config/mongrel_cluster.yml --clean --only 8010" if failed host 127.0.0.1 port 8010 with timeout 10 seconds then restart if totalmem > 128 Mb then restart if cpu is greater than 60% for 2 cycles then alert if 3 restarts within 5 cycles then timeout group mongrel
The start/stop commands work perfectly from the command line, but somehow not when monit’s calling them. Sure enough, you find this in the mongrel.8010.log file:
/usr/lib/ruby/gems/1.8/gems/rubyforge-1.0.3/lib/rubyforge.rb:15:in `expand_path': couldn't find HOME environment -- expanding `~' (ArgumentError)
The line in question is
HOME = ENV["HOME"] || ENV["HOMEPATH"] || File::expand_path("~")
Monit does not set a HOME environment variable, nor HOMEPATH.
The documentation for File::expand_path says:
Converts a pathname to an absolute pathname. Relative paths are referenced from the current working directory of the process unless dir_string is given, in which case it will be used as the starting point. The given pathname may start with a ``~’’, which expands to the process owner‘s home directory (the environment variable HOME must be set correctly). ``~user’’ expands to the named user‘s home directory.
Ouch. So if HOME is not set, File::expand_path(“~”) is guaranteed to fail. That’s a bug in the rubyforge gem I think.
I worked around this by setting ENV["HOME"] to a fallback value before the
line in /usr/bin/mongrel_rails.