Settings in sysctl.d not being applied at boot

[mani001]

Hi,

I have a file 10-inotify.conf in /etc/sysctl.d/ to try and set the filesystem's max_user_watches:

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root@aguarrioquad sysctl.d $bat -p 10-inotify.conf 
fs.inotify.max_user_watches = 524288

but it seems this is not read at boot

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root@aguarrioquad sysctl.d $bat -p /proc/sys/fs/inotify/max_user_watches 
16384

However, if I restart the sysctl systemd service

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systemctl restart systemd-sysctl.service

then it is read

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root@aguarrioquad sysctl.d $bat -p /proc/sys/fs/inotify/max_user_watches 
524288

However, it seems that systemd-sysctl.service is a service that is enabled by default

root@aguarrioquad sysctl.d $systemctl enable systemd-sysctl.service
The unit files have no installation config (WantedBy=, RequiredBy=, Also=,
Alias= settings in the [Install] section, and DefaultInstance= for template
units). This means they are not meant to be enabled using systemctl.

Possible reasons for having this kind of units are:
• A unit may be statically enabled by being symlinked from another unit's
.wants/ or .requires/ directory.
• A unit's purpose may be to act as a helper for some other unit which has
a requirement dependency on it.
• A unit may be started when needed via activation (socket, path, timer,
D-Bus, udev, scripted systemctl call, ...).
• In case of template units, the unit is meant to be enabled with some
instance name specified.

This only happens to me in one of my machines, so it's kind of weird...

Any clue?

[toralf]

Does this

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$> rc-update | grep sysctl
               sysctl | boot     

looks similar at your system ?

[mani001]

I don't have rc-update in my system. I guess it's because I use systemd and rc-update is an OpenRC thing (right?). An analogous thing might be:

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root@aguarrioquad ~ $systemctl list-unit-files | grep sysctl
systemd-sysctl.service                                    static          -

[Etal]

Are you sure it's not being overridden elsewhere? Your number looks suspiciously low and square.

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$ grep -r max_user_watches /etc/sysctl.*

What does it show when you get the status?

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$ systemctl status systemd-sysctl
● systemd-sysctl.service - Apply Kernel Variables
     Loaded: loaded (/lib/systemd/system/systemd-sysctl.service; static)
     Active: active (exited) since Fri 2022-06-17 21:56:40 EDT; 2 days ago
       Docs: man:systemd-sysctl.service(8)
             man:sysctl.d(5)
    Process: 321 ExecStart=/lib/systemd/systemd-sysctl (code=exited, status=0/SUCCESS)
   Main PID: 321 (code=exited, status=0/SUCCESS)
        CPU: 3ms

Jun 17 21:56:40 xxx systemd[1]: Finished Apply Kernel Variables.

[mani001]

Are you sure it's not being overridden elsewhere?

I had also though of that...but, unfortunately, that's not it

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root@aguarrioquad ~ $grep -r max_user_watches /etc/sysctl.*
/etc/sysctl.d/10-inotify.conf:fs.inotify.max_user_watches = 524288

I even though whether it might be something taking precedence (it shouldn't) in the system's sysctl directory

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root@aguarrioquad ~ $grep -r max_user_watches /usr/lib/sysctl.d/*
root@aguarrioquad ~ $

but no.

About the suspicious number, I agree...no idea, probably some old default value hardcoded somewhere (by the way, 16384 is 2 to the 14 => a 14 bits field...not that it helps, but whatever )

systemd reports everything is fine

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root@aguarrioquad ~ $systemctl status systemd-sysctl 
● systemd-sysctl.service - Apply Kernel Variables
     Loaded: loaded (/lib/systemd/system/systemd-sysctl.service; static)
     Active: active (exited) since Mon 2022-06-20 20:29:20 CEST; 2min 1s ago
       Docs: man:systemd-sysctl.service(8)
             man:sysctl.d(5)
    Process: 136 ExecStart=/lib/systemd/systemd-sysctl (code=exited, status=0/SUCCESS)
   Main PID: 136 (code=exited, status=0/SUCCESS)
        CPU: 7ms

[Etal]

Does restarting it apply the value?

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systemctl restart systemd-sysctl

Do you see the config/value printed if you run this?

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/lib/systemd/systemd-sysctl --cat-config

[mani001]

Does restarting it apply the value?

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systemctl restart systemd-sysctl	

Yes

Do you see the config/value printed if you run this?

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/lib/systemd/systemd-sysctl --cat-config

Yes

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root@aguarrioquad ~ $/lib/systemd/systemd-sysctl --cat-config
# /lib/sysctl.d/00protected-links.conf
fs.protected_symlinks = 1
fs.protected_hardlinks = 1

# /etc/sysctl.d/10-inotify.conf
fs.inotify.max_user_watches = 524288

# /usr/lib/sysctl.d/50-coredump.conf
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

# See sysctl.d(5) for the description of the files in this directory.
...

[Etal]

Hmm, so it sounds like systemd-sysctl picks up the values and applies them, you can verify by setting some other tunable in 10-inotify.conf and see if it gets picked up. But then something else must be overriding it afterwards…

Some obscure service? Something in tmpfiles.d? A user log in script calling sudo?

[mani001]

Hmm, so it sounds like systemd-sysctl picks up the values and applies them, you can verify by setting some other tunable in 10-inotify.conf and see if it gets picked up. But then something else must be overriding it afterwards…

You are probably right, I just added

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fs.inotify.max_user_instances = 129

to the same sysctl.d file, and it gets properly set at boot