systemctl access denied when root

Question

When I run

sudo systemctl disable avahi-daemon.socket

I get

Failed to execute operation: Access denied

But it's run as root, how can access be denied? (CentOS 7)

Solution 1

I also work on CentOS 7, and had a similar issue:

# systemctl unmask tmp.mount
Failed to execute operation: Access denied

The denial has to do with SELinux. This can be your case if you are running SELinux in enforcing mode:

# getenforce
Enforcing

In my case, the systemctl error had produced an USER_AVC denial in SELinux log file, /var/log/audit/audit.log:

type=USER_AVC msg=audit(1475497680.859:2656): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='avc:  denied  { enable } for auid=0 uid=0 gid=0 path="/dev/null" cmdline="systemctl unmask tmp.mount" scontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tcontext=system_u:object_r:null_device_t:s0 tclass=service  exe="/usr/lib/systemd/systemd" sauid=0 hostname=? addr=? terminal=?'

Solution

This article states that it is due to a bug in systemd, and provides a work around:

systemctl daemon-reexec

Secondary solution

If the above did not work, you can set SELinux mode to permissive:

setenforce 0

and it should work fine. However, this 2nd solution has security implications.

Solution 2

In my case, I had just upgraded systemd and any systemctl command was failing:

# systemctl daemon-reexec
Failed to reload daemon: Access denied
# systemctl status
Failed to read server status: Access denied

However according to the init manpage, you can do the same thing by sending SIGTERM to the daemon running as PID 1, which worked:

kill -TERM 1

This reloaded the daemon, after which all the systemctl commands started working again.

Solution 3

Neither solution worked for me. It turned out there was a missing = sign on one of the lines in my .service file. I discovered this by looking /var/log/messages and saw an error there that was more descriptive. So the Access Denied was misleading. It was not a really a security problem.

Comments

[spraff]

I get no output instead of Removed symlink and afterwards systemctl disable avahi-daemon.socket fails as before, producing the same line in audit.log

[Elouan Keryell-Even]

Can you try to disable selinux enforce mode? setenforce 0

[spraff]

systemctl disable avahi-daemon.socket succeeds after setenforce 0 without systemctl daemon-reexec (and I realise now the unmask is your command, not mine :-)) Is it okay to just do this and setenforce 1 after?

[Elouan Keryell-Even]

@spraff I don't know, I'm a SELinux newbie ha ha. Imma mention setenforce 0 in my answer then.

[user1130976]

@spraff you can run setenforce 1 after. that resets it to enforce.

[Ramhound]

You should provide more detail on how you solve this question. For instance you talk about a more verbose error message, but do not indicate, what the error messag was exactly. Without this information, this would be better served as a comment, because this answer without this information is incomplete.

[Younes]

Please don't setenforce 0. This is a bad practice in production environment. Please use systemctl daemon-reexec instead.

[Pancho Jay]

systemctl daemon-reexec worked on RHEL 7.4.

[aaaaaa]

systemctl daemon-reexec did not work for me, I'm on fedora 28. setenforce 0 did work. Normally I'm against these security hacks but I'm swimming in my own hair out of frustration with working with nonsense apis such as 'daemon-reexec' and 'setenforce 0'. What does setenforce 0 do? Why it sets the enforce status to permissive of course!

[rogerdpack]

which log file showed the message?

[buergi]

Thanks. Solved my problem I had after upgrading an archlinux distro after a long time.

[Roy Shilkrot]

worked on Ubuntu 18.10 - Thanks!

[gwik]

Same issue while force dist-upgrading ubuntu cosmic. Worked, thx.

[Rebs]

It appears this is triggered by any invalid syntax in the file (not just the = as you mention). Double check your service files for errors if you see this.

[Muhammad Mehran Khan Attari]

It worked on Ubuntu 20.04 (upgraded from 18.10) and saved me a ton of headaches. Bundle of thanks

[sodimel]

Tried to upgrade lubuntu 18.10 to lubuntu 20.04 and had this error with whoopsi service. The systemctl daemon-reexec did the trick, thanks :)

[4t8dds]

I got the same issue. I upgraded my OS and then systemctl did not work for me. And this helps. Thanks. My version is centOS 8.