How to use svlogd with dinit?

[ArchGuyWu]

I'm using dinit in Termux.

My service description file for svlogd:

type = process
command = $PREFIX/lib/dinit/user/svlogd -tt $PREFIX/var/log/dinit/user/$1
restart = on-failure
smooth-recovery = yes
after: local.target
log-type = buffer
consumer-of = $1

@include-opt $PREFIX/etc/dinit.d/user/config/svlogd@$1.override

Its shell wrapper script:

#!/data/data/com.termux/files/usr/bin/sh
mkdir -p "$2"
exec $PREFIX/bin/busybox svlogd "$1" "$2"

But I got this warning:

svlogd: warning: can't lock directory: /data/data/com.termux/files/usr/var/log/dinit/user/sshd: Try again
svlogd: fatal: no functional log directories
(dinit: note: service restarted)

[mobin-2008]

Hi. I think there is something wrong with directory permissions because of svlogd: warning: can't lock directory: /data/data/com.termux/files/usr/var/log/dinit/user/sshd: Try again line. Can you create lock file in the created directory?

Context: https://git.busybox.net/busybox/tree/runit/svlogd.c?h=1_37_stable#n726

[davmac314]

@mobin-2008 once again if you're not sure please don't answer. Stop giving out potentially incorrect information.

@ArchGuyWu "Try again" is likely the error message from EAGAIN meaning that the directory is already locked. Are you sure there's nothing already locking the directory? Maybe the service process is already running before you try to start the service via dinit?

[ArchGuyWu]

And there's no issue if I run $PREFIX/bin/busybox svlogd "$1" "$2" in command line.

[davmac314]

I comfired that this lock file is created by svlogd itself

Looking at the code for svlogd (see link Mobin posted above) it is:

• opening the file using open with O_NDELAY (and with O_CREAT, so this should create the file)
• then, if successful, locking it use flock (with LOCK_NB).

Either of those need to fail with EAGAIN (AKA EWOULDBLOCK) for you to see that error message ("Try again"). For both those cases, the file would need to already be locked to get the error (and that means it already has to exist). So I don't think there's any way that Dinit itself can cause the error.

This feels like a race condition. Perhaps try adding a sleep 1 in the start script to see if just adding a delay makes a difference.

[ArchGuyWu]

I comfired that this lock file is created by svlogd itself

Looking at the code for svlogd (see link Mobin posted above) it is:

• opening the file using open with O_NDELAY (and with O_CREAT, so this should create the file)
• then, if successful, locking it use flock (with LOCK_NB).

Either of those need to fail with EAGAIN (AKA EWOULDBLOCK) for you to see that error message ("Try again"). For both those cases, the file would need to already be locked to get the error (and that means it already has to exist). So I don't think there's any way that Dinit itself can cause the error.

This feels like a race condition. Perhaps try adding a sleep 1 in the start script to see if just adding a delay makes a difference.

Adding a delay works, but the starting log is lost.

[davmac314]

What do you mean "the starting log is lost"?

[davmac314]

Anyway the fact that adding a delay prevents the problem strongly suggests that you have another service process that is trying to log to the same directory.