SYS-PCTL(2) SYS-PCTL(2) NAME pctl - process control SYNOPSIS include "sys.m"; sys := load Sys Sys->PATH; pctl: fn(flags: int, movefd: list of int): int; DESCRIPTION A newly spawned Limbo process (also known as a thread) shares with its parent process a number of resources and properties, such as file name space, open file descriptors, current working directory, and so on. Pctl controls this sharing, allowing a process to gain a copy of a resource rather than to share it, to start with a null resource, and so on. The set of processes sharing a property are called a group; for example the set of processes sharing a name space are called a name space group. Each process is a member of a process group, typically the set of threads functioning as a single program. All the members of a process group may be terminated at once using the killgrp control message in the prog(3) device. A call to pctl affects the calling process and, indirectly according to flags, any other processes sharing properties with it. The flags to pctl are: NEWFD Give the process a new file descriptor group. All file descriptors are closed except those listed in movefd, which are preserved in the new group. After this call, changes the process makes to its set of open file descriptors will not be visible to other processes. FORKFD Place the process in a new file descriptor group containing a copy of the current set of file descriptors. The file descriptors listed in movefd are closed in the old group. After this call, changes the process makes to its set of open file descriptors will not be visible to other processes. NEWNS Place the process in a new file name space group in which the current directory is made the root direc- tory, `/', of the new name space. The current directory is unaffected by this call. SYS-PCTL(2) SYS-PCTL(2) FORKNS Place the process in a new file name space group containing a copy of the current name space. After this call, changes the process makes to its name space, including chdir calls, will not affect other processes. NODEVS Set the current file name space group to prevent subsequent access to the roots of file trees imple- mented by a device driver (ie, the use of path names beginning with #, as described by intro(3)). Even after NODEVS the following devices can be attached, which are either private or can be separately controlled: pipe(3), env(3), srv(3) and ssl(3). NEWENV Place the process in a new empty environment group containing no environment variables. After this call, changes the process makes to its environment will not affect other processes. FORKENV Place the process in a new environment group con- taining a copy of the current environment vari- ables. After this call, changes the process makes to its environment will not affect other processes. NEWPGRP Establish a new process group with a group id equal to that of the pid of the calling process. The Inferno shell sh(1) uses FORKFD when starting a command; its pctl built-in (see sh-std(1)) can invoke the other effects when needed. The window manager wm(1) uses NEWPGRP|FORKFD when starting a window manager application. A network server might use NEWPGRP|FORKNS|FORKFD|FORKENV to insulate itself completely from services it starts. The return value of pctl is the numerical process id of the calling process, which can be used for example to access its prog(3) files. SEE ALSO sh-std(1), sys-intro(2)