Bug 90185 - RFE: allow assigning the empty string to a setting to reset it to the default (example: StandardOutput)
Summary: RFE: allow assigning the empty string to a setting to reset it to the default...
Status: NEW
Alias: None
Product: systemd
Classification: Unclassified
Component: general (show other bugs)
Version: unspecified
Hardware: x86-64 (AMD64) Linux (All)
: medium normal
Assignee: systemd-bugs
QA Contact: systemd-bugs
Depends on:
Reported: 2015-04-26 15:53 UTC by Alain Kalker
Modified: 2015-04-27 13:28 UTC (History)
0 users

See Also:
i915 platform:
i915 features:


Description Alain Kalker 2015-04-26 15:53:17 UTC
Steps to reproduce:

- Create a drop-in file to override StandardInput= StandardOutput= StandardError= as set in a service and restore them to their default values.

Example (here I'm trying to debug why keyboard doesn't work in emergency mode, not the best example, I know...):
# Clear ExecStartPre=
# Are the tty,std{in,out,error} devices there?
ExecStartPre=-/usr/bin/ls -la /dev
ExecStartPre=-/bin/echo -e 'Welcome to emergency mode! After logging in, type "journalctl -xb" to view\\nsystem logs, "systemctl reboot" to reboot, "systemctl default" or ^D to\\ntry again to boot into default mode.'

# Clear these out to defaults, see what happens...
# StandardInput=tty-force
# StandardOutput=inherit
# StandardError=inherit
# Don't know about the next one, don't touch it for now
# IgnoreSIGPIPE=no

Actual result:

[    0.506012] systemd[1]: [/etc/systemd/system/emergency.service.d/debug.conf:10] Failed to parse input specifier, ignoring: 
[    0.506865] systemd[1]: [/etc/systemd/system/emergency.service.d/debug.conf:12] Failed to parse output specifier, ignoring: 
[    0.507699] systemd[1]: [/etc/systemd/system/emergency.service.d/debug.conf:14] Failed to parse output specifier, ignoring: 

Expected result:

Setting these directives to the empty value in a drop-in should set them to their default values.

Requiring users to explicitly specify that default value is IMHO not a good option, as that default might change over the course of the development of systemd. There should always be a way for drop-ins to 'undo' setting a directive done by a service, no matter what it is.
Comment 1 Zbigniew Jedrzejewski-Szmek 2015-04-26 16:06:21 UTC
Yes, unsetting those settings is not possible in this way. Unsetting is only supported for a subset of directives.
Comment 2 Alain Kalker 2015-04-26 16:18:22 UTC
Ah, I see. A pity, because that means that drop-ins may need updating when defaults change.
Thanks for the quick reply :-)
Comment 3 Lennart Poettering 2015-04-27 13:28:28 UTC
This is currently not supported for any of our settings. Assigning the empty string to a setting only applies to settings that take lists of things, and will reset those lists to the empty list.

Using this as a way to reset things to the default value might make sense, admittedly.

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