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JAIL(2)                  DragonFly System Calls Manual                 JAIL(2)


jail -- imprison current process and future descendants


Standard C Library (libc, -lc)


#include <sys/types.h> #include <sys/jail.h> int jail(struct jail *jail);


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; uint32_t n_ips; struct sockaddr_storage *ips; }; ``version'' defines the version of the API in use. It should be set to 1 at this time. 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. ``n_ips'' is the number of IP addresses that are on ips. The ``ips'' pointer contains the IP addresses assigned to the jail.


Once a process has been put in a prison, it and its descendants cannot escape the prison. A process can be attached to a prison by calling jail_attach(2). Inside the prison, the concept of "superuser" is very diluted. In gen- eral, 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 can- not be created because they reference shared resources (the device driv- ers in the kernel). All IP activity will be forced to happen to/from the IP numbers speci- fied, which should be an alias on one or more of the network interfaces. 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 cur- rently set for the prison for jailed processes. The program jls(8) ca be used to identify all active jails.


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


The jail() system call will fail if: [EINVAL] The version number of the argument is not correct. Further 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), jail_attach(2), jail(8), jexec(8), jls(8)


The jail() function call appeared in FreeBSD 4.0.


The jail feature was written by Poul-Henning Kamp for R&D Associates ``http://www.rndassociates.com/'' who contributed it to FreeBSD. DragonFly 3.5 April 28, 1999 DragonFly 3.5

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