[TBD]Understanding systemd

Introduction

Laymen explanation

Technical explanation

Useful commands

Troubleshooting

Where to see the log

Use journalctl or systemctl

journelctl example output

root@ubuntu:~/personal/jeffk/cpx# journalctl -xe

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

--

-- Unit docker.service has finished shutting down.

Dec 12 19:16:58 ubuntu systemd[1]: Closed Docker Socket for the API.

-- Subject: Unit docker.socket has finished shutting down

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

--

-- Unit docker.socket has finished shutting down.

Dec 12 19:16:58 ubuntu systemd[1]: Stopping Docker Socket for the API.

-- Subject: Unit docker.socket has begun shutting down

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

--

-- Unit docker.socket has begun shutting down.

Dec 12 19:16:58 ubuntu systemd[1]: Starting Docker Socket for the API.

-- Subject: Unit docker.socket has begun start-up

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

--

-- Unit docker.socket has begun starting up.

Dec 12 19:16:58 ubuntu systemd[1]: Listening on Docker Socket for the API.

-- Subject: Unit docker.socket has finished start-up

-- Defined-By: systemd

-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel

--

-- Unit docker.socket has finished starting up.

--

-- The start-up result is done.

Dec 12 19:16:58 ubuntu systemd[1]: docker.service: Start request repeated too quickly.

Dec 12 19:16:58 ubuntu systemd[1]: Failed to start Docker Application Container Engine.

-- Subject: Unit docker.service has failed

....

systemctl example output

root@ubuntu:~/personal/jeffk/cpx# systemctl status docker.service

● docker.service - Docker Application Container Engine

Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)

Drop-In: /etc/systemd/system/docker.service.d

└─hosts.conf

Active: inactive (dead) (Result: exit-code) since Tue 2017-12-12 19:22:32 IST; 45s ago

Docs: https://docs.docker.com

Process: 14147 ExecStart=/usr/bin/dockerd -H fd:// -H tcp://0.0.0.0:2736 (code=exited, status=1/FAILURE)

Main PID: 14147 (code=exited, status=1/FAILURE)

Dec 12 19:22:32 ubuntu systemd[1]: docker.service: Main process exited, code=exited, status=1/FAILURE

Dec 12 19:22:32 ubuntu systemd[1]: Failed to start Docker Application Container Engine.

Dec 12 19:22:32 ubuntu systemd[1]: docker.service: Unit entered failed state.

Dec 12 19:22:32 ubuntu systemd[1]: docker.service: Failed with result 'exit-code'.

Dec 12 19:22:32 ubuntu systemd[1]: docker.service: Service hold-off time over, scheduling restart.

Dec 12 19:22:32 ubuntu systemd[1]: Stopped Docker Application Container Engine.

Dec 12 19:22:32 ubuntu systemd[1]: docker.service: Start request repeated too quickly.

Dec 12 19:22:32 ubuntu systemd[1]: Failed to start Docker Application Container Engine.

Dec 12 19:23:15 ubuntu systemd[1]: Stopped Docker Application Container Engine.

root@ubuntu:~/personal/jeffk/cpx#

Handling error in log "docker.service: Start request repeated too quickly"

The default limit is to allow 5 restarts in a 10sec period. If a service goes over that threshold due to the Restart= config option in the service definition, it will not attempt to restart any further.

Ratelimit on number of restart attempt for a service

Refer man systemd.unit and man systemd.service

Useful link: https://serverfault.com/questions/845471/service-start-request-repeated-too-quickly-refusing-to-start-limit

Reference

https://serverfault.com/questions/845471/service-start-request-repeated-too-quickly-refusing-to-start-limit