freebsd/usr.sbin/chroot/chroot.8

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.Dd July 20, 2021
.Dt CHROOT 8
.Os
.Sh NAME
.Nm chroot
.Nd change root directory
.Sh SYNOPSIS
.Nm
.Op Fl G Ar group Ns Op Cm \&, Ns Ar group  ...
.Op Fl g Ar group
.Op Fl u Ar user
.Op Fl n
.Ar newroot
.Op Ar command Op Ar arg ...
.Sh DESCRIPTION
The
.Nm
utility changes its current and root directories to the supplied directory
.Ar newroot
and then exec's
.Ar command
with provided arguments, if supplied,
or an interactive copy of the user's login shell.
.Pp
The options are as follows:
.Bl -tag -width "-G group[,group ...]"
.It Fl G Ar group Ns Op Cm \&, Ns Ar group  ...
Run the command with the permissions of the specified groups.
.It Fl g Ar group
Run the command with the permissions of the specified
.Ar group .
.It Fl u Ar user
Run the command as the
.Ar user .
.It Fl n
Use the
.Dv PROC_NO_NEW_PRIVS_CTL
.Xr procctl 2
command before chrooting, effectively disabling SUID/SGID bits
for the calling process and its descendants.
If
.Dv security.bsd.unprivileged_chroot
sysctl is set to 1, it will make it possible to chroot without
superuser privileges.
.El
.Sh ENVIRONMENT
The following environment variable is referenced by
.Nm :
.Bl -tag -width "SHELL"
.It Ev SHELL
If set,
the string specified by
.Ev SHELL
is interpreted as the name of
the shell to exec.
If the variable
.Ev SHELL
is not set,
.Pa /bin/sh
is used.
.El
.Sh EXAMPLES
.Bl -tag -width 0n
.It Sy Example 1\&: No Chrooting into a New Root Directory
.Pp
The following command opens the
.Xr csh 1
shell after chrooting to the standard root directory.
.Bd -literal -offset 2n
.Li # Ic chroot / /bin/csh
.Ed
.It Sy Example 2\&: No Execution of a Command with a Changed Root Directory
.Pp
The following command changes a root directory with
.Nm
and then runs
.Xr ls 1
to list the contents of
.Pa /sbin .
.Bd -literal -offset 2n
.Li # Ic chroot /tmp/testroot ls /sbin
.Ed
.El
.Sh SEE ALSO
.Xr chdir 2 ,
.Xr chroot 2 ,
.Xr setgid 2 ,
.Xr setgroups 2 ,
.Xr setuid 2 ,
.Xr getgrnam 3 ,
.Xr environ 7 ,
.Xr jail 8
.Sh HISTORY
The
.Nm
utility first appeared in
.At III
and
.Bx 4.3 Reno .