How to have a systemd service programmatically stop its-self? Even if Restart=always is set? Thus, any exit code returned, the service is restarted? If my service stops with exit code 0, Restart=always should not be invoked? How to mimic 'systemctl stop' from within the service its self?
Related
I have the following script:
whie true
do
#code
sleep 60
done
I then wanted to create a service to start the machine and launch this script as service:
created my.service at /etc/systemd/system/my.service
[Unit]
Description=my Script
[Service]
Type=forking
ExecStart=/bin/script.sh
[Install]
WantedBy=multi-user.target
problem occurs when i systemctl start my.service
it goes to while true loop and hang in there, how can i run this service and make it run in the background ?
According to systemd specification at link. Type=forking is not exactly correct kind of start-up in your case
If set to forking, it is expected that the process configured with
ExecStart= will call fork() as part of its start-up. The parent
process is expected to exit when start-up is complete and all
communication channels are set up. The child continues to run as the
main service process, and the service manager will consider the unit
started when the parent process exits. This is the behavior of
traditional UNIX services. If this setting is used, it is recommended
to also use the PIDFile= option, so that systemd can reliably identify
the main process of the service. systemd will proceed with starting
follow-up units as soon as the parent process exits.
The Type=simple can be correct one. You can try with it
If set to simple (the default if ExecStart= is specified but neither
Type= nor BusName= are), the service manager will consider the unit
started immediately after the main service process has been forked
off. It is expected that the process configured with ExecStart= is the
main process of the service. In this mode, if the process offers
functionality to other processes on the system, its communication
channels should be installed before the service is started up (e.g.
sockets set up by systemd, via socket activation), as the service
manager will immediately proceed starting follow-up units, right after
creating the main service process, and before executing the service's
binary. Note that this means systemctl start command lines for simple
services will report success even if the service's binary cannot be
invoked successfully (for example because the selected User= doesn't
exist, or the service binary is missing).
I would like systemd to manage the tup monitor, so I wrote a service unit:
[Unit]
Description=Monitor source files for changes
[Service]
Type=simple
ExecStart=/usr/bin/tup monitor -f
ExecStop=/usr/bin/tup stop
WorkingDirectory=/some/dir
StandardOutput=journal+console
StandardError=journal+console
[Install]
WantedBy=multi-user.target
Whereas starting the monitor manually works, trying to do it with systemd fails with the following error:
setpgid: Operation not permitted
tup error: Unable to set process group for tup's subprocesses.
The error originates in this file and seems to be due to systemd not giving the process the capabilities it needs, so I went further:
[Unit]
Description=Monitor source files for changes
[Service]
Type=simple
ExecStart=/usr/bin/tup monitor -f
ExecStop=/usr/bin/tup stop
CapabilityBoundingSet=CAP_SETUID CAP_SETGID
AmbientCapabilities=CAP_SETUID CAP_SETGID
WorkingDirectory=/some/dir
StandardOutput=journal+console
StandardError=journal+console
[Install]
WantedBy=multi-user.target
Still, it doesn't work.
How can I tell systemd to keep the permissions tup requires?
systemd does not restrict any permissions on services by default, so I don’t think that’s the problem. The setpgid(2) manpage mentions three possible conditions for EPERM, though:
An attempt was made to move a process into a process group in a different session, or to change the process group ID of one of the children of the calling process and the child was in a different session, or to change the process group ID of a session leader (setpgid(), setpgrp()).
I think the third one is the most likely cause of the error: tup probably expects to be run from a shell, in which case the shell would be the session leader and tup tries to establish its own process group, but systemd places each service in its own session as part of setting up a clean execution environment for the service (see also daemon(7)), so that step fails.
Unless you can somehow disable that step in tup (it doesn’t need to fork, either, or do a number of other things which systemd makes unnecessary), I think the only workaround would be an ugly hack:
ExecStart=/bin/sh -c '/usr/bin/tup monitor -f'
With this, the session leader will be the shell, not tup, so the setpgid should work again.
Try this
[Unit]
Description=Monitor source files for changes
After=network.target
[Service]
Type=simple
ExecStart=/usr/bin/tup monitor -f
ExecStop=/usr/bin/tup stop
CapabilityBoundingSet=CAP_SETUID CAP_SETGID
AmbientCapabilities=CAP_SETUID CAP_SETGID
WorkingDirectory=/some/dir
StandardOutput=journal+console
StandardError=journal+console
[Install]
WantedBy=multi-user.target
I've added After=network.target, this will make sure TUP service starts after the network is fully active and avoid the service failing due to network issues
When googling around for different oneshot systemd unit files I often stumble upon this kind of file:
[Unit]
Description=/etc/rc.local Compatibility
After=network.target
[Service]
Type=oneshot
ExecStart=-/etc/rc.local
ExecStart=-/pathtoyour/script1
ExecStart=-/pathtoyour/script2
TimeoutSec=0
StandardInput=tty <======= WHAT'S THIS?
RemainAfterExit=yes <======= WHAT'S THIS?
[Install]
WantedBy=multi-user.target
See unclear points inline in the example.
StandardInput=tty means that started scripts' standard input is connected to a TTY (by default /dev/console, if no other are specified through "TTYPath=")
RemainAfterExit=yes means that service shall be considered active even when all its processes exited.
See here for more information: https://www.freedesktop.org/software/systemd/man/systemd.directives.html
Is there some way to trigger an event (e.g. running a script to push some logs to S3) when an EC2 instance is stopped/terminated?
I have looked into triggering the script using a service in /usr/lib/systemd/system but I haven't had any luck with that yet. I have heard that networking capabilities on the instance can be shutdown before a service is triggered and if true, that could be why the script is not executing correctly.
So the answer is not really AWS specific, but it is working for me now (tested on EC2 instance stopping and terminating).
I've created a system.d service file:
/usr/lib/systemd/system/my_shutdown.service
[Unit]
Description=my_shutdown Service
Before=shutdown.target reboot.target halt.target
Requires=network-online.target network.target
[Service]
KillMode=none
ExecStart=/bin/true
ExecStop=/path/to/my_script.sh
RemainAfterExit=yes
Type=oneshot
[Install]
WantedBy=multi-user.target
Added this service to multi-user.target:
systemctl enable my_shutdown.service
Alternatively you can manually create the symlink:
ln -s /usr/lib/systemd/system/my_shutdown.service /etc/systemd/system/multi-user.target.wants/my_shutdown.service
Started the service and tested by stopping/terminating the instance.
systemctl start my_shutdown.service
My understanding:
Description: a description of our service.
Before: we want our service to stop before these targets are started.
Requires: our service requires that network capabilities are available. These targets must not be stopped before our service starts/stops.
KillMode: none; do not kill our process.
ExecStart: /bin/true; a command that does nothing but returns a success. Run when are service is started.
ExecStop: the script to run. Run when are service is being stopped.
RemainAfterExit: consider our service active even when all its processes exited.
Type: oneshot; it is expected that the process has to exit before systemd starts follow-up units.
WantedBy: the target we want to add our service to.
References:
https://www.freedesktop.org/software/systemd/man/systemd.service.html
https://www.freedesktop.org/software/systemd/man/systemd.kill.html#
https://www.freedesktop.org/software/systemd/man/systemd.special.html
https://www.freedesktop.org/software/systemd/man/systemd.target.html
You can trigger events, such as pushing logs to S3 on specific events, with CloudWatch... Learn more here: https://aws.amazon.com/cloudwatch/
I am new to systemd service scripts. I am trying to start my application from systemd service scripts. My application is a process that in turn invokes multiple process that includes Qt GUI as one of its child. But the service downt starting up my application.
This is how my service looks like:
[Unit]
Description=/etc/rc.d/rc.local Compatibility
ConditionFileIsExecutable=/etc/rc.d/rc.local
After=network.target
[Service]
Type=forking
ExecStart=/etc/rc.d/rc.local start
SysVStartPriority=99
rc.local script looks like:
#!/bin/bash
export DISPLAY=:0
sleep 5
cd /var/MINC3/apps
./PMonTsk
So when try to run the command "systemctl start rc-local.service", the command executes the script but doesnt invoke my application. If I replace some other QT GUI sample application in the plcae of my application in rc.local, it is working fine. Please help me on sorting this issue.
If you add
[Install]
WantedBy=multi-user.target
I think it will work ;)
I found solution for the above problem. I modified my service in the following way. It works fine after the modification.
[Unit]
Description=/etc/rc.d/rc.local Compatibility
ConditionFileIsExecutable=/etc/rc.d/rc.local
After=network.target
[Service]
Type=forking
ExecStart=/etc/rc.d/rc.local start
ControlGroup=cpu:/
SysVStartPriority=99