Langue: en

Version: 265919 (debian - 07/07/09)

Section: 2 (Appels système)

BSD mandoc


jail , jail_attach - imprison current process and future descendants


Lb libc


In sys/param.h In sys/jail.h Ft int Fn jail struct jail *jail Ft int Fn jail_attach int jid


The Fn jail system call sets up a jail and locks the current process in it.

The argument is a pointer to a structure describing the prison:

 struct jail {
         u_int32_t       version;
         char            *path;
         char            *hostname;
         char            *jailname;
         unsigned int    ip4s;
         unsigned int    ip6s;
         struct in_addr  *ip4;
         struct in6_addr *ip6;

``version '' defines the version of the API in use. JAIL_API_VERSION is defined for the current version.

The ``path '' pointer should be set to the directory which is to be the root of the prison.

The ``hostname '' pointer can be set to the hostname of the prison. This can be changed from the inside of the prison.

The ``jailname '' pointer is an optional name that can be assigned to the jail for example for managment purposes.

The ``ip4s '' and ``ip6s '' give the numbers of IPv4 and IPv6 addresses that will be passed via their respective pointers.

The ``ip4 '' and ``ip6 '' pointers can be set to an arrays of IPv4 and IPv6 addresses to be assigned to the prison, or NULL if none. IPv4 addresses must be in network byte order.

The Fn jail_attach system call attaches the current process to an existing jail, identified by Fa jid .


If successful, Fn jail returns a non-negative integer, termed the jail identifier (JID). It returns -1 on failure, and sets errno to indicate the error.

Rv -std jail_attach


Once a process has been put in a prison, it and its descendants cannot escape the prison.

Inside the prison, the concept of ``superuser'' is very diluted. In general, it can be assumed that nothing can be mangled from inside a prison which does not exist entirely inside that prison. For instance the directory tree below ``path '' can be manipulated all the ways a root can normally do it, including ``rm -rf /* '' but new device special nodes cannot be created because they reference shared resources (the device drivers in the kernel). The effective ``securelevel'' for a process is the greater of the global ``securelevel'' or, if present, the per-jail ``securelevel''

All IP activity will be forced to happen to/from the IP number specified, which should be an alias on one of the network interfaces. All connections to/from the loopback address ( for IPv4, ::1 for IPv6) will be changed to be to/from the primary address of the jail for the given address family.

It is possible to identify a process as jailed by examining ``/proc/<pid>/status '' it will show a field near the end of the line, either as a single hyphen for a process at large, or the hostname currently set for the prison for jailed processes.


The Fn jail system call will fail if:
The version number of the argument is not correct.

Further Fn jail calls chroot(2) internally, so it can fail for all the same reasons. Please consult the chroot(2) manual page for details.


chdir(2), chroot(2)


The Fn jail system call appeared in Fx 4.0 . The Fn jail_attach system call appeared in Fx 5.1 .


The jail feature was written by An Poul-Henning Kamp for R&D Associates ``http://www.rndassociates.com/ '' who contributed it to Fx .