--- name: "jail" section: "2freebsd" platform: "linux" package: "freebsd-manpages" version: "12.2-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/jail/2freebsd" --- # jail(2freebsd) create and manage system jails ## NAME **jail**, **jail\_get**, **jail\_set**, **jail\_remove**, **jail\_attach** – create and manage system jails ## LIBRARY Standard C Library (libc, -lc) ## SYNOPSIS **#include \** **#include \** *int*\ **jail**(*struct jail \*jail*); *int*\ **jail\_attach**(*int jid*); *int*\ **jail\_remove**(*int jid*); **#include \** *int*\ **jail\_get**(*struct iovec \*iov*, *u\_int niov*, *int flags*); *int*\ **jail\_set**(*struct iovec \*iov*, *u\_int niov*, *int flags*); ## DESCRIPTION The **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 { uint32_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 management 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. This is equivalent to, and deprecated in favor of, the **jail\_set**() system call (see below), with the parameters *path*, *host.hostname*, *name*, *ip4.addr*, and *ip6.addr*, and with the JAIL\_ATTACH flag. The **jail\_set**() system call creates a new jail, or modifies an existing one, and optionally locks the current process in it. Jail parameters are passed as an array of name-value pairs in the array *iov*, containing *niov* elements. Parameter names are a null-terminated string, and values may be strings, integers, or other arbitrary data. Some parameters are boolean, and do not have a value (their length is zero) but are set by the name alone with or without a “no” prefix, e.g. *persist* or *nopersist*. Any parameters not set will be given default values, generally based on the current environment. Jails have a set of core parameters, and modules can add their own jail parameters. The current set of available parameters, and their formats, can be retrieved via the *security.jail.param* sysctl MIB entry. Notable parameters include those mentioned in the **jail**() description above, as well as *jid* and *name*, which identify the jail being created or modified. See [jail(8)](/jail/8.md) for more information on the core jail parameters. The *flags* arguments consists of one or more of the following flags: - JAIL\_CREATE Create a new jail. If a *jid* or *name* parameters exists, they must not refer to an existing jail. - JAIL\_UPDATE Modify an existing jail. One of the *jid* or *name* parameters must exist, and must refer to an existing jail. If both JAIL\_CREATE and JAIL\_UPDATE are set, a jail will be created if it does not yet exist, and modified if it does exist. - JAIL\_ATTACH In addition to creating or modifying the jail, attach the current process to it, as with the **jail\_attach**() system call. - JAIL\_DYING Allow setting a jail that is in the process of being removed. The **jail\_get**() system call retrieves jail parameters, using the same name-value list as **jail\_set**() in the *iov* and *niov* arguments. The jail to read can be specified by either *jid* or *name* by including those parameters in the list. If they are included but are not intended to be the search key, they should be cleared (zero and the empty string respectively). The special parameter *lastjid* can be used to retrieve a list of all jails. It will fetch the jail with the jid above and closest to the passed value. The first jail (usually but not always jid 1) can be found by passing a *lastjid* of zero. The *flags* arguments consists of one or more following flags: - JAIL\_DYING Allow getting a jail that is in the process of being removed. The **jail\_attach**() system call attaches the current process to an existing jail, identified by *jid*. The **jail\_remove**() system call removes the jail identified by *jid*. It will kill all processes belonging to the jail, and remove any children of that jail. ## RETURN VALUES If successful, **jail**(), **jail\_set**(), and **jail\_get**() return a non-negative integer, termed the jail identifier (JID). They return -1 on failure, and set *errno* to indicate the error. The **jail\_attach()** and **jail\_remove()** functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ## ERRORS The **jail**() system call will fail if: - \[EPERM\] This process is not allowed to create a jail, either because it is not the super-user, or because it would exceed the jail's *children.max* limit. - \[EFAULT\] *jail* points to an address outside the allocated address space of the process. - \[EINVAL\] The version number of the argument is not correct. - \[EAGAIN\] No free JID could be found. The **jail\_set**() system call will fail if: - \[EPERM\] This process is not allowed to create a jail, either because it is not the super-user, or because it would exceed the jail's *children.max* limit. - \[EPERM\] A jail parameter was set to a less restrictive value then the current environment. - \[EFAULT\] *Iov*, or one of the addresses contained within it, points to an address outside the allocated address space of the process. - \[ENOENT\] The jail referred to by a *jid* or *name* parameter does not exist, and the JAIL\_CREATE flag is not set. - \[ENOENT\] The jail referred to by a *jid* is not accessible by the process, because the process is in a different jail. - \[EEXIST\] The jail referred to by a *jid* or *name* parameter exists, and the JAIL\_UPDATE flag is not set. - \[EINVAL\] A supplied parameter is the wrong size. - \[EINVAL\] A supplied parameter is out of range. - \[EINVAL\] A supplied string parameter is not null-terminated. - \[EINVAL\] A supplied parameter name does not match any known parameters. - \[EINVAL\] One of the JAIL\_CREATE or JAIL\_UPDATE flags is not set. - \[ENAMETOOLONG\] A supplied string parameter is longer than allowed. - \[EAGAIN\] There are no jail IDs left. The **jail\_get**() system call will fail if: - \[EFAULT\] *Iov*, or one of the addresses contained within it, points to an address outside the allocated address space of the process. - \[ENOENT\] The jail referred to by a *jid* or *name* parameter does not exist. - \[ENOENT\] The jail referred to by a *jid* is not accessible by the process, because the process is in a different jail. - \[ENOENT\] The *lastjid* parameter is greater than the highest current jail ID. - \[EINVAL\] A supplied parameter is the wrong size. - \[EINVAL\] A supplied parameter name does not match any known parameters. The **jail\_attach**() and **jail\_remove**() system calls will fail if: - \[EPERM\] A user other than the super-user attempted to attach to or remove a jail. - \[EINVAL\] The jail specified by *jid* does not exist. Further **jail**(), **jail\_set**(), and **jail\_attach**() call [chroot(2)](/chroot/2.md) internally, so they can fail for all the same reasons. Please consult the [chroot(2)](/chroot/2.md) manual page for details. ## SEE ALSO [chdir(2)](/chdir/2.md), [chroot(2)](/chroot/2.md), [jail(8)](/jail/8.md) ## HISTORY The **jail**() system call appeared in FreeBSD 4.0. The **jail\_attach**() system call appeared in FreeBSD 5.1. The **jail\_set**(), **jail\_get**(), and **jail\_remove**() system calls appeared in FreeBSD 8.0. ## AUTHORS The jail feature was written by Poul-Henning Kamp for R&D Associates who contributed it to FreeBSD. James Gritton added the extensible jail parameters and hierarchical jails.