Running Redis in daemonized form and using Upstart to manage it doesn't work

Question

I've written an Upstart script for Redis as follows:

description "Redis Server"

start on runlevel [2345]
stop on shutdown
expect daemon

exec sudo -u redis /usr/local/bin/redis-server /etc/redis/redis.conf

respawn
respawn limit 10 5

I then configure redis via it's redis.conf to:

daemonize yes

All the documentation and my own experimentation says Redis forks twice in daemonized form and "expect daemon" should work, but the Upstart script is always holding on to the PID of the former parent (PID - 1). Has anyone got this working?

Answer 1

The following upstart config seems to be working for me, with upstart 1.5 on ubuntu 12.04, with redis.conf daemonize set to yes:

description "redis server"

start on (local-filesystems and net-device-up IFACE=eth0)
stop on shutdown

setuid redis
setgid redis
expect fork

exec /opt/redis/redis-server /opt/redis/redis.conf

respawn

Answer 2

Other people have the same problem. See this gist.

When the daemonize option is activated, Redis does not check if the process is already a daemon (there is no call to getppid). It systematically forks, but only once. It is somewhat unusual, other daemonization mechanisms may require the initial check on getppid, and fork to be called twice (before and after the setsid call), but on Linux this is not strictly required.

See this faq for more information about daemonization.

Redis daemonize function is extremely simple:

void daemonize(void) {
    int fd;

    if (fork() != 0) exit(0); /* parent exits */
    setsid(); /* create a new session */

    /* Every output goes to /dev/null. If Redis is daemonized but
     * the 'logfile' is set to 'stdout' in the configuration file
     * it will not log at all. */
    if ((fd = open("/dev/null", O_RDWR, 0)) != -1) {
        dup2(fd, STDIN_FILENO);
        dup2(fd, STDOUT_FILENO);
        dup2(fd, STDERR_FILENO);
        if (fd > STDERR_FILENO) close(fd);
    }
}

Upstart documentation says:

expect daemon
Specifies that the job's main process is a daemon, and will fork twice after being run.
init(8) will follow this daemonisation, and will wait for this to occur before running
the job's post-start script or considering the job to be running.
Without this stanza init(8) is unable to supervise daemon processes and will
believe them to have stopped as soon as they daemonise on startup.

expect fork
Specifies that the job's main process will fork once after being run. init(8) will
follow this fork, and will wait for this to occur before running the job's post-start
script or considering the job to be running.
Without this stanza init(8) is unable to supervise forking processes and will believe
them to have stopped as soon as they fork on startup.

So I would either deactivate daemonization on Redis side, either try to use expect fork rather than expect daemon in upstart configuration.