#1124679 systemd-sysusers rejects usernames with dots that adduser allows, breaking package installations

Package:
systemd
Source:
systemd
Description:
system and service manager
Submitter:
Samuel Verstraete
Date:
2026-01-05 14:23:03 UTC
Severity:
normal
#1124679#5
Date:
2026-01-05 14:19:44 UTC
From:
To:
Dear Maintainer,

   * What led up to the situation?
   Debian's adduser/useradd tools allow creating usernames containing dots (e.g.,
  "samuel.verstraete"), which are valid POSIX usernames.  However, systemd-sysusers
  enforces stricter validation rules that reject these same usernames, causing
  packages that use sysusers.d configuration files to fail during installation.
   * Steps to Reproduce:
   1. Create a user with a dot in the username:
   sudo adduser samuel.verstraete

   2. Install a package that uses systemd-sysusers to add this user to a group
   (e.g., firezone-client-gui)

   3. The package post-installation fails with:
   /usr/lib/sysusers.d/firezone-client-tunnel.conf:5: 'samuel.verstraete' is
   not a valid user or group name.

   * Expected Behaviour:
   If Debian's user management tools allow creating users with dots in their names,
   systemd-sysusers should also accept these usernames. The system should be
   internally consistent - core tools should not reject what other core tools create.

   * Actual Behaviour:
   systemd-sysusers validation regex appears to be:  ^[a-z_][a-z0-9_-]*\$? $
   This rejects dots and uppercase letters that adduser allows.

   * User Information:
   - User exists and is valid:
     $ whoami
     samuel.verstraete

     $ id
     uid=1001(samuel.verstraete) gid=1001(samuel.verstraete) groups=1001(samuel.verstraete),...

   - systemd-sysusers rejects this valid username in sysusers.d files