How systemd exponential restart delay works

Since the beginning, systemd had a Restart= directive to do just that – restart a service when it fails or exists. Some tuning was provided by RestartSec= (how long to wait between restarts), StartLimitBurst= (how many times to try) and few minor directives.

Starting with systemd v254, we have two new knobs:

• RestartSteps= the number of steps to take to increase the interval of auto-restarts

• RestartMaxDelaySec= the longest time to sleep before restarting a service as the interval goes up

Together, they provide ability to exponentially extend wait-time between restarts. First restart is quite quick, but then system waits more and more. Here what it means.

Let assume a service with following settings:

Restart=always
RestartSec=100ms (the default)
RestartMaxDelaySec=10s
RestartSteps=5

Upon a failure, systemd will wait (rounded a bit):

0. 100ms until first restart

1. 250ms until next restart (first step)

2. 630ms until next restart (second step)

3. 1.58s until next restart (third step)

4. 3.98s until next restart (fourth step)

5. 10.0s until next restart (RestartSteps=5 – fifth step) and following restarts

Second example. Given:

RestartSec=1s
RestartMaxDelaySec=10s
RestartSteps=3

subsequent restarts will be done after waiting:

0. 100ms

1. 2.15s (step 1)

2. 4.64s (step 2)

3. 10.0s (step 3, as in RestartSteps=3).

Hope this helps. You can find the exact formula in src/core/service.c.