table of contents
|CHROOT(2)||System Calls Manual||CHROOT(2)|
chroot — change
Standard C Library (libc, -lc)
The dirname argument is the address of the
pathname of a directory, terminated by an ASCII NUL. The
system call causes dirname to become the root
directory, that is, the starting point for path searches of pathnames
beginning with ‘
In order for a directory to become the root directory a process must have execute (search) access for that directory.
It should be noted that
has no effect on the process's current directory.
This call is restricted to the super-user.
Depending on the setting of the
sysctl variable, open filedescriptors which reference directories will make
fail as follows:
is set to zero,
will always fail with
EPERM if there are any
is set to one (the default),
will fail with
EPERM if there are any directories
open and the process is already subject to the
chroot() system call.
Any other value for
will bypass the check for open directories
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
chroot() system call will fail and the
root directory will be unchanged if:
- A component of the path name is not a directory.
- The effective user ID is not the super-user, or one or more filedescriptors are open directories.
- A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
- The named directory does not exist.
- Search permission is denied for any component of the path name.
- Too many symbolic links were encountered in translating the pathname.
- The dirname argument points outside the process's allocated address space.
- An I/O error occurred while reading from or writing to the file system.
- Corrupted data was detected while reading from the file system.
chroot() system call appeared in
Version 7 AT&T UNIX. It was marked as
“legacy” in Version 2 of the Single
UNIX Specification (“SUSv2”), and was removed in
If the process is able to change its working directory to the target directory, but another access control check fails (such as a check for open directories, or a MAC check), it is possible that this system call may return an error, with the working directory of the process left changed.
The system have many hardcoded paths to files where it may load
after the process starts. It is generally recommended to drop privileges
immediately after a successful
chroot call, and
restrict write access to a limited subtree of the
chroot root, for instance, setup the sandbox so that
the sandboxed user will have no write access to any well-known system
|June 26, 2020||Debian|