How can I log the stdout of a process started by start-stop-daemon?

Question

To expand on ypocat's answer, since it won't let me comment:

start-stop-daemon --start --quiet --chuid $DAEMONUSER    \
 --make-pidfile --pidfile $PIDFILE --background       \
 --startas /bin/bash -- -c "exec $DAEMON $DAEMON_ARGS > /var/log/some.log 2>&1"

Using exec to run the daemon allows stop to correctly stop the child process instead of just the bash parent.

Using --startas instead of --exec ensures that the process will be correctly detected by its pid and won't erroneously start multiple instances of the daemon if start is called multiple times. Otherwise, start-stop-daemon will look for a /bin/bash process and ignore the actual child process running the daemon.

You need to do:

start-stop-daemon --start --quiet --chuid $DAEMONUSER    \
    --make-pidfile --pidfile $PIDFILE --background       \
    --exec /bin/bash -- -c "$DAEMON $DAEMON_ARGS > /var/log/some.log 2>&1"

Also if you use --chuid or --user, make sure the user can write to /var/log or the existing /var/log/some.log. The best way is to have that user own a /var/log/subdir/ though.

It seems you should be able to use now the --no-close parameter when starting start-stop-daemon to capture the daemon output. This new feature is available in the dpkg package since version 1.16.5 on Debian:

Add new --no-close option to disable closing fds on --background.

This enabled the caller to see process messages for debugging purposes, or to be able to redirect file descriptors to log files, syslog or similar.

With openrc (which is the default on gentoo or alpine linux for instance) start-stop-daemon has the -1 and -2 options:

-1, --stdout Redirect stdout to file

-2, --stderr Redirect stderr to file

So you can just write:

start-stop-daemon --start --quiet --chuid $DAEMONUSER    \
    --make-pidfile --pidfile $PIDFILE --background       \
    --exec $DAEMON $DAEMON_ARGS -1 $LOGFILE -2 $LOGFILE