Gnome Desktop Manager fails to start if /proc is mounted with hidepid=1.

This document (7023519) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15

Situation

Starting with SLES 12 (or Linux kernel 3.3) the kernel has two new mount options for the /proc file system. 
  • hidepid: controls whether to hide or not the content inside /proc. 
  • gid: defines a group that will be able to gather all processes' info. 
hidepid can have three values: 
  • 0 ; (default) all users can read all world-readable /proc/PID/* files.
  • 1 ; users may not access any /proc/<pid>/ directories, but their own. 
  • 2 ; means hidepid=1 plus all /proc/PID/ will be invisible to other users.
For security reasons, if server was configured to mount /proc with hidepid=1 ; Gnome Display Manager (GDM) may fail to startup. 
With error messages similar to what is listed below : 

2018-11-09T10:38:19.148175+01:00 srv01 gdm-x-session: Preparing auth file for X server
2018-11-09T10:38:19.148268+01:00 srv01 gdm-x-session: Running X server
2018-11-09T10:38:19.178031+01:00 srv01 systemd[1]: Started Process Core Dump (PID 6441/UID 0).
2018-11-09T10:38:19.207996+01:00 srv01 gdm-x-session: X server did not write display string
2018-11-09T10:38:19.208502+01:00 srv01 gdm-launch-environment]: GdmSessionWorker: child (pid:6438) done (status:70)
2018-11-09T10:38:19.208684+01:00 srv01 gdm-launch-environment]: GdmSessionWorker: uninitializing PAM
2018-11-09T10:38:19.209302+01:00 srv01 gdm-launch-environment]: pam_unix(gdm-launch-environment:session): session closed for user gdm
2018-11-09T10:38:19.209980+01:00 srv01 gdm-launch-environment]: GdmSessionWorker: jumping to VT 1
2018-11-09T10:38:19.222660+01:00 srv01 gdm-launch-environment]: GdmSessionWorker: couldn't finalize jump to VT 1: Interrupted system call
2018-11-09T10:38:19.222887+01:00 srv01 gdm-launch-environment]: GdmSessionWorker: state NONE
2018-11-09T10:38:19.223025+01:00 srv01 gdm: GdmSession: Emitting 'session-exited' signal with exit code '70'


Resolution

To fix this issue: 
  • Create a new group 
  • Add all users that need to read '/proc' filesystem into that group (including the 'gdm' user) 
  • Create the file '/etc/systemd/system/systemd-logind.conf.d/hidepid.conf' with the below information (replace '<NEW_GROUP>' with the above group): 
[Service]
SupplementaryGroups=<NEW_GROUP>
  • Remount the '/proc' file system with gid: 
mount -o remount,hidepid=1,gid=<NEW_GROUP_ID> /proc
  • Restart GDM : 
systemctl restart display-manager.service

GDM should start normally. 

Cause

systemd-logind doesn't have full read access to the '/proc' file system. 

Additional Information

For more information about hidepid option, please read this commit from kernel.org site. 

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:7023519
  • Creation Date: 14-Nov-2018
  • Modified Date:03-Mar-2020
    • SUSE Linux Enterprise Server

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