Re: [CentOS] systemd and 'Stale file handle' errors?

Jonathan Billings wrote:

So, the chronyd systemd unit looks like this:

# /usr/lib/systemd/system/chronyd.service
[Unit]
Description=NTP client/server
Documentation=man:chronyd(8) man:chrony.conf(5)
After=ntpdate.service sntp.service ntpd.service
Conflicts=ntpd.service systemd-timesyncd.service
ConditionCapability=CAP_SYS_TIME

[Service]
Type=forking
PIDFile=/var/run/chrony/chronyd.pid
EnvironmentFile=-/etc/sysconfig/chronyd
ExecStart=/usr/sbin/chronyd $OPTIONS
ExecStartPost=/usr/libexec/chrony-helper update-daemon
PrivateTmp=yes
ProtectHome=yes
ProtectSystem=full

[Install]
WantedBy=multi-user.target

So, you'll notice there are "ProtectHome=yes" and "ProtectSystem=yes" settings in the Service section. This sets up a private namespace for the systemd unit so /home, /root and /run/user are made inaccessible and empty (ProtectHome), and /usr, /boot and /etc are read-only (ProtectSystem). It does this to reduce the ability of a malicious NTP server attacking the system through bogus NTP traffic (which is a real thing that can happen). Many systemd services limit their processes this way.

I suspect that is why you're seeing stale file handle errors, the kernel can't set up the namespace for directories that are now stale on the system.

You can probably just do a lazy unmount (umount -l) to make them go away until you reboot. You can also disable the namespaced directories by doing a 'systemctl edit chronyd.service' and setting the options to 'off', but you'll be reducing the security of your system.

Thanks - that all makes sense - unfortunately 'umount -l' didn't work :-(

I've actually now rebooted the box - but if something like this happens again, maybe I could use a drop-in snippet in /run/systemd/system/ to turn the options off - which would then only last until the next reboot ?

Thanks

James Pearson