[Bug 1931630] [NEW] Linux images for virtual machines with unset `CONFIG_MAGIC_SYSRQ` cause `10-magic-sysrq.conf` to fail

[Paul Menzel]

Public bug reported:

*procps* ships `/etc/sysctl.d/10-magic-sysrq.conf:kernel.sysrq = 176`,
which is run by `systemd-sysctl.service`. This fails on a system run
with a Linux image built for virtual machines *linux-image-kvm*, which
has `CONFIG_MAGIC_SYSRQ` not set.

```
$ sudo /lib/systemd/systemd-sysctl
Couldn't write '176' to 'kernel/sysrq', ignoring: No such file or directory
Not setting net/ipv4/conf/all/promote_secondaries (explicit setting exists).
Not setting net/ipv4/conf/default/promote_secondaries (explicit setting exists).
Couldn't write 'fq_codel' to 'net/core/default_qdisc', ignoring: No such file or directory
Couldn't write '4194304' to 'kernel/pid_max': Invalid argument
$ grep SYSRQ /boot/config-5.4.0-1009-kvm
# CONFIG_MAGIC_SYSRQ is not set
```

** Affects: procps (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1931630

Title:
  Linux images for virtual machines with unset `CONFIG_MAGIC_SYSRQ`
  cause `10-magic-sysrq.conf` to fail

Status in procps package in Ubuntu:
  New

Bug description:
  *procps* ships `/etc/sysctl.d/10-magic-sysrq.conf:kernel.sysrq = 176`,
  which is run by `systemd-sysctl.service`. This fails on a system run
  with a Linux image built for virtual machines *linux-image-kvm*, which
  has `CONFIG_MAGIC_SYSRQ` not set.

  ```
  $ sudo /lib/systemd/systemd-sysctl
  Couldn't write '176' to 'kernel/sysrq', ignoring: No such file or directory
  Not setting net/ipv4/conf/all/promote_secondaries (explicit setting exists).
  Not setting net/ipv4/conf/default/promote_secondaries (explicit setting exists).
  Couldn't write 'fq_codel' to 'net/core/default_qdisc', ignoring: No such file or directory
  Couldn't write '4194304' to 'kernel/pid_max': Invalid argument
  $ grep SYSRQ /boot/config-5.4.0-1009-kvm
  # CONFIG_MAGIC_SYSRQ is not set
  ```

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