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.Dd February 28, 2026
.Dt LINUX-VERSION 1
.Os
.Sh NAME
.Nm linux-version
.Nd print the installed system and kernel version on Linux
.Sh SYNOPSIS
.Nm
.Op Fl kru
.Op Fl j Ar jail
.Sh DESCRIPTION
The
.Nm
utility is a Linux-native port of
.Xr freebsd-version 1
for this repository.
It reports the installed kernel version,
the running kernel version,
and the installed userland version.
.Pp
The following options are available:
.Bl -tag -width Fl
.It Fl k
Print the installed kernel version for the target root.
On Linux, this is resolved from the default kernel symlink
.Pa /vmlinuz
or
.Pa /boot/vmlinuz
when available,
otherwise from a unique kernel release under
.Pa /lib/modules
or
.Pa /usr/lib/modules .
If several installed kernels exist and no default boot target can be
determined, the command fails with an explicit error.
.It Fl r
Print the running kernel version from
.Pa /proc/sys/kernel/osrelease .
.It Fl u
Print the installed userland version from
.Pa /etc/os-release
or
.Pa /usr/lib/os-release
under the target root.
The utility prefers
.Ev VERSION_ID ,
then falls back to
.Ev BUILD_ID ,
.Ev VERSION ,
and
.Ev PRETTY_NAME .
.It Fl j Ar jail
Accepted for interface compatibility but not supported on Linux.
The command exits with an explicit error because Linux containers and
namespaces do not provide a jail-equivalent query with compatible semantics.
.El
.Pp
If several supported options are specified,
.Nm
prints the installed kernel version first,
then the running kernel version,
and finally the installed userland version,
each on a separate line.
If no option is specified,
it prints the installed userland version only.
.Sh ENVIRONMENT
.Bl -tag -width ROOT
.It Ev ROOT
Path to the root of the filesystem tree in which to inspect
.Pa os-release ,
.Pa /boot/vmlinuz ,
and kernel module directories for
.Fl k
and
.Fl u .
This does not affect
.Fl r ,
which always reports the current running kernel.
.El
.Sh IMPLEMENTATION NOTES
This port intentionally does not preserve FreeBSD-specific implementation
details such as parsing
.Pa loader.conf ,
querying
.Va kern.osrelease
via
.Xr sysctl 8 ,
or executing inside jails with
.Xr jexec 8 .
.Pp
The Linux kernel does not provide a syscall or procfs interface that reports
the installed-on-disk kernel version separately from the running kernel.
Therefore
.Nm
uses the default kernel symlink when present and otherwise requires a unique
kernel release under the module tree.
.Sh SEE ALSO
.Xr uname 1 ,
.Xr os-release 5