ProtectHostname setting
The property ProtectHostname is a systemd unit setting used for sandboxing. It is available since systemd 242.
Purpose: defines if hostname or NIS domain name can be changed
Why and when to use ProtectHostname
Systemd provides the unit setting ProtectHostname to restrict changing the hostname of the system. This makes use of the UTS namespace, which defines the hostname and NIS domain name. The hostname can normally be changed using the syscall sethostname(2), while the NIS domain name has the related setdomainname(2) syscall. If the the ProtectHostname setting is active (boolean yes or true), a new UTS namespace is created that prevents making any changes.
The creation of a new UTS namespace is done using clone(2) or unshare(2) syscall with the CLONE_NEWUTS flag set. This functionality requires a Linux kernel that is compiled with the CONFIG_UTS_NS option.
Syscalls of interest are:
- sethostname
- setdomainname
If a program contains these system calls, then additional research is needed if ProtectHostname can be used safely.
Generic advice
Setting the hostname is rarely needed, so most services can be configured with ProtectHostname=yes.
Values
Systemd unit setting ProtectHostname expects a boolean (yes/no or true/false) or string value.
| Value | Intended action | Available since systemd version |
|---|---|---|
| no | normal behavior of hostname changes - default | 242 |
| yes | no changes to hostname or NIS domain name allowed | 242 |
Example to show the current value of ProtectHostname for the ssh service:
systemctl show --property=ProtectHostname ssh.serviceRelated hardening profiles
The systemd unit setting ProtectHostname is used in the following systemd hardening profiles. These hardening profiles help improving security of common Linux services and usually require minimal tuning.
