.TH SYS-PCTL 2.SH NAMEpctl \- process control.SH SYNOPSIS.EXinclude "sys.m";sys := load Sys Sys->PATH; pctl: fn(flags: int, movefd: list of int): int;.EE.SH DESCRIPTIONA 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 Pctlcontrols this sharing, allowing a process to gain a copy of a resourcerather than to share it, to start with a null resource, and so on..PPThe 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 groupmay be terminated at once using the.B killgrpcontrol message in the.IR prog (3)device..PPA call to.B pctlaffects the calling process and, indirectly according to.IR flags ,any other processes sharing properties with it.The.I flagsto.B pctlare:.TF FORKENV.PD.TP.B NEWFDGive 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 descriptorswill not be visible to other processes..TP.B FORKFDPlace the process in a new file descriptor groupcontaining a copyof the current set of file descriptors.The file descriptors listed in.I movefdare closed in the.I oldgroup.After this call, changes the process makes to its set of open file descriptorswill not be visible to other processes..TP.B NEWNSPlace the process in a new file name space group in which the current directoryis made the root directory,.LR / ,of the new name space.The current directory is unaffected by this call..TP.B FORKNSPlace the process in a new file name space groupcontaining a copyof the current name space.After this call, changes the process makes to its name space, including.B chdircalls,will not affect other processes..TP.B NODEVSSet the current file name space group to prevent subsequent access tothe roots of file trees implemented by a device driver (ie, the use of pathnames beginning with.BR # ,as described by.IR intro (3)).Even after.B NODEVSthe following devices can be attached, which are eitherprivate or can be separately controlled:.IR pipe (3) ,.IR env (3),.IR srv (3)and.IR ssl (3)..TP .B NEWENVPlace the process in a new empty environment group containingno environment variables.After this call, changes the process makes to its environment willnot affect other processes..TP .B FORKENVPlace the process in a new environment group containinga copy of the current environment variables.After this call, changes the process makes to its environment willnot affect other processes..TP.B NEWPGRPEstablish a new process group with a group id equal to that of the pidof the calling process..PPThe Inferno shell.IR sh (1)uses.B FORKFDwhen starting a command;its.I pctlbuilt-in (see.IR sh-std (1))can invoke the other effects when needed.The window manager.IR wm (1)uses.B NEWPGRP|FORKFDwhen starting a window manager application..IR Srv (8)uses.B NEWGRP|FORKNS|FORKFDto insulate itself completely from services it starts..PPThe return value of.B pctlis the numerical process id of  the calling process, which can be used for example toaccess its.IR prog (3)files..SH SEE ALSO.IR sh-std (1),.IR sys-intro (2)