shithub: purgatorio

ref: bd6c2aad586814b091ce5aca9d41cf2c51adb37b
dir: /man/2/sys-pctl/

.TH SYS-PCTL 2
.SH NAME
pctl \- process control
.SH SYNOPSIS
.EX
include "sys.m";
sys := load Sys Sys->PATH;

pctl: fn(flags: int, movefd: list of int): int;
.EE
.SH 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.
.B 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.
.PP
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
.IR "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
.B killgrp
control message in the
.IR prog (3)
device.
.PP
A call to
.B pctl
affects the calling process and, indirectly according to
.IR flags ,
any other processes sharing properties with it.
The
.I flags
to
.B pctl
are:
.TF FORKENV
.PD
.TP
.B NEWFD
Give the process a new file descriptor group.
All file descriptors are closed except those listed in
.IR 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.
.TP
.B 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
.I movefd
are closed in the
.I old
group.
After this call, changes the process makes to its set of open file descriptors
will not be visible to other processes.
.TP
.B NEWNS
Place the process in a new file name space group in which the current directory
is made the root directory,
.LR / ,
of the new name space.
The current directory is unaffected by this call.
.TP
.B 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
.B chdir
calls,
will not affect other processes.
.TP
.B NODEVS
Set the current file name space group to prevent subsequent access to
the roots of file trees implemented by a device driver (ie, the use of path
names beginning with
.BR # ,
as described by
.IR intro (3)).
Even after
.B NODEVS
the following devices can be attached, which are either
private or can be separately controlled:
.IR pipe (3) ,
.IR env (3),
.IR srv (3)
and
.IR ssl (3).
.TP 
.B 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.
.TP 
.B FORKENV
Place the process in a new environment group containing
a copy of the current environment variables.
After this call, changes the process makes to its environment will
not affect other processes.
.TP
.B NEWPGRP
Establish a new process group with a group id equal to that of the pid
of the calling process.
.PP
The Inferno shell
.IR sh (1)
uses
.B FORKFD
when starting a command;
its
.I pctl
built-in (see
.IR sh-std (1))
can invoke the other effects when needed.
The window manager
.IR wm (1)
uses
.B NEWPGRP|FORKFD
when starting a window manager application.
A network server might use
.B NEWPGRP|FORKNS|FORKFD|FORKENV
to insulate itself completely from services it starts.
.PP
The return value of
.B pctl
is the numerical process id of  the calling process, which can be used for example to
access its
.IR prog (3)
files.
.SH SEE ALSO
.IR sh-std (1),
.IR sys-intro (2)