Monit check file fails for character device files

[Jef Driesen]

I have a daemon which depends on the presence of a hardware device. If that hardware is not present, the daemon is not started and should not be monitored either. To solve this problem, I check for the presence of the device node as follows:

check file myservice-device with path /dev/mydevice
    if does not exist then unmonitor
    group devices

check process myservice with pidfile /var/run/myservice.pid
    start program = "/etc/init.d/myservice start"
    stop program = "/etc/init.d/myservice stop"
    if does not exist for 2 cycles then restart
    depends on myservice-device
    group services

This works great for regular files (e.g. config files), but in this particular case the /dev/mydevice is a symlink to the actual device node:

# stat /dev/mydevice
  File: /dev/mydevice -> ttyUSB1
  Size: 7               Blocks: 0          IO Block: 4096   symbolic link
Device: 6h/6d   Inode: 2904        Links: 1
Access: (0777/lrwxrwxrwx)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2018-11-23 06:40:23.296368326 +0000
Modify: 1970-01-01 00:00:08.124385375 +0000
Change: 1970-01-01 00:00:08.124385375 +0000
 Birth: -

And that seems to cause the check to fail with "Invalid type":

# monit status myservice-device
Monit 5.23.0 uptime: 17h 23m

File 'myservice-device'
  status                       Invalid type
  monitoring status            Monitored
  monitoring mode              active
  on reboot                    start
  permission                   660
  uid                          0
  gid                          20
  size                         0 B
  access timestamp             Thu, 22 Nov 2018 15:01:45
  change timestamp             Thu, 01 Jan 1970 00:00:08
  modify timestamp             Thu, 22 Nov 2018 15:01:45
  data collected               Fri, 23 Nov 2018 08:22:34

Is there a way to let monit to follow the symlink?

[Jef Driesen]

It seems the problem is not the symlink, but the fact that the file it references is a character device:

# stat /dev/ttyUSB1
  File: /dev/ttyUSB1
  Size: 0           Blocks: 0          IO Block: 4096   character special file
Device: 6h/6d   Inode: 2857        Links: 1     Device type: bc,1
Access: (0660/crw-rw----)  Uid: (    0/    root)   Gid: (   20/ dialout)
Access: 2018-11-29 07:39:55.990000000 +0000
Modify: 2018-11-29 07:39:54.990000000 +0000
Change: 2018-11-28 14:22:15.990000000 +0000
 Birth: -

[Jef Driesen]

The attached patch fixes the problem for me.

[Divyesh Surana]

When will this enhancement be a part of a release?