113 lines
3.1 KiB
Groff
113 lines
3.1 KiB
Groff
.\"
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.\" This manual page is taken directly from Plan9, and modified to
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.\" describe the actual BSD implementation. Permission for
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.\" use of this page comes from Rob Pike <rob@plan9.att.com>.
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.\"
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.Dd Jan 12, 1996
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.Dt RFORK 2
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.Os
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.Sh NAME
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.Nm rfork
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.Nd manipulate process resources
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.Sh SYNOPSIS
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.Fd #include <unistd.h>
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.Ft int
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.Fn rfork "int flags"
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.Sh DESCRIPTION
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Forking, vforking or rforking is the only way new processes are created.
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The
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.Fa flags
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argument to
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.Fn rfork
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selects which resources of the
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invoking process (parent) are shared
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by the new process (child) or initialized to
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their default values.
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The resources include
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the open file descriptor table (which, when shared, permits processes
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to open and close files for other processes),
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and open files.
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.Fa Flags
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is the logical OR of some subset of
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.Bl -tag -width "RFCNAMEG" -compact -offset indent
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.It RFPROC
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If set a new process is created; otherwise changes affect the
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current process.
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The current implementation requires this flag to always be set.
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.It RFNOWAIT
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If set, the child process will be dissociated from the parent. Upon
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exit the child will not leave a status for the parent to collect.
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See
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.Xr wait 2 .
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This is not currently implemented.
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.It RFNAMEG, RFCNAMEG, RFENVG, RFCENVG, RFNOTEG
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These are Plan 9 specific flags, and not implemented.
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.It RFFDG
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If set, the invoker's file descriptor table (see
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.Xr intro 2
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) is copied; otherwise the two processes share a
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single table.
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.It RFCFDG
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If set, the new process starts with a clean file descriptor table.
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Is mutually exclusive with
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.Dv RFFDG .
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.It RFMEM
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If set, the kernel will force sharing of the entire address space.
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The child
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will then inherit all the shared segments the parent process owns. Other segment
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types will be unaffected. Subsequent forks by the parent will then
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propagate the shared data and bss between children. The stack segment
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is always split. May be set only with
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.Dv RFPROC .
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.El
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.Pp
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File descriptors in a shared file descriptor table are kept
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open until either they are explicitly closed
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or all processes sharing the table exit.
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.Pp
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If
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.Dv RFPROC
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is set, the
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value returned in the parent process
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is the process id
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of the child process; the value returned in the child is zero.
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Without
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.Dv RFPROC ,
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the return value is zero.
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Process id's range from 1 to the maximum integer
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.Ft ( int )
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value.
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.Fn Rfork
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will sleep, if necessary, until required process resources are available.
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.Pp
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.Fn Fork
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can be implemented as a call to
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.Xr rfork "RFFDG|RFPROC"
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but isn't for backwards compatibility.
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.Sh ERRORS
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.Fn Rfork
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will fail and no child process will be created if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The system-imposed limit on the total
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number of processes under execution would be exceeded.
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This limit is configuration-dependent.
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.It Bq Er EAGAIN
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The system-imposed limit
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.Dv MAXUPRC
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.Pq Aq Pa sys/param.h
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on the total number of
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processes under execution by a single user would be exceeded.
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.It Bq Er ENOMEM
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There is insufficient swap space for the new process.
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.El
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.Sh SEE ALSO
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.Xr intro 2 ,
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.Xr fork 2 ,
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.Xr vfork 2 ,
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.Xr minherit 2
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.Sh HISTORY
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The
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.Fn rfork
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function first appeared in Plan9.
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