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+.\" Copyright (c) 1983, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"	@(#)1.1.t	8.1 (Berkeley) 6/8/93
+.\"
+.sh "Processes and protection
+.NH 3
+Host and process identifiers
+.PP
+Each UNIX host has associated with it a 32-bit host id, and a host
+name of up to 64 characters (as defined by MAXHOSTNAMELEN in
+\fI<sys/param.h>\fP).
+These are set (by a privileged user)
+and returned by the calls:
+.DS
+sethostid(hostid)
+long hostid;
+
+hostid = gethostid();
+result long hostid;
+
+sethostname(name, len)
+char *name; int len;
+
+len = gethostname(buf, buflen)
+result int len; result char *buf; int buflen;
+.DE
+On each host runs a set of \fIprocesses\fP.
+Each process is largely independent of other processes,
+having its own protection domain, address space, timers, and
+an independent set of references to system or user implemented objects.
+.PP
+Each process in a host is named by an integer
+called the \fIprocess id\fP.  This number is
+in the range 1-30000
+and is returned by
+the \fIgetpid\fP routine:
+.DS
+pid = getpid();
+result int pid;
+.DE
+On each UNIX host this identifier is guaranteed to be unique;
+in a multi-host environment, the (hostid, process id) pairs are
+guaranteed unique.
+.NH 3
+Process creation and termination
+.PP
+A new process is created by making a logical duplicate of an
+existing process:
+.DS
+pid = fork();
+result int pid;
+.DE
+The \fIfork\fP call returns twice, once in the parent process, where
+\fIpid\fP is the process identifier of the child,
+and once in the child process where \fIpid\fP is 0.
+The parent-child relationship induces a hierarchical structure on
+the set of processes in the system.
+.PP
+A process may terminate by executing an \fIexit\fP call:
+.DS
+exit(status)
+int status;
+.DE
+returning 8 bits of exit status to its parent.
+.PP
+When a child process exits or
+terminates abnormally, the parent process receives
+information about any
+event which caused termination of the child process.  A
+second call provides a non-blocking interface and may also be used
+to retrieve information about resources consumed by the process during its
+lifetime.
+.DS
+#include <sys/wait.h>
+
+pid = wait(astatus);
+result int pid; result union wait *astatus;
+
+pid = wait3(astatus, options, arusage);
+result int pid; result union waitstatus *astatus;
+int options; result struct rusage *arusage;
+.DE
+.PP
+A process can overlay itself with the memory image of another process,
+passing the newly created process a set of parameters, using the call:
+.DS
+execve(name, argv, envp)
+char *name, **argv, **envp;
+.DE
+The specified \fIname\fP must be a file which is in a format recognized
+by the system, either a binary executable file or a file which causes
+the execution of a specified interpreter program to process its contents.
+.NH 3
+User and group ids
+.PP
+Each process in the system has associated with it two user-id's:
+a \fIreal user id\fP and a \fIeffective user id\fP, both 16 bit
+unsigned integers (type \fBuid_t\fP).
+Each process has an \fIreal accounting group id\fP and an \fIeffective
+accounting group id\fP and a set of
+\fIaccess group id's\fP.  The group id's are 16 bit unsigned integers
+(type \fBgid_t\fP).
+Each process may be in several different access groups, with the maximum
+concurrent number of access groups a system compilation parameter,
+the constant NGROUPS in the file \fI<sys/param.h>\fP,
+guaranteed to be at least 8.
+.PP
+The real and effective user ids associated with a process are returned by:
+.DS
+ruid = getuid();
+result uid_t ruid;
+
+euid = geteuid();
+result uid_t euid;
+.DE
+the real and effective accounting group ids by:
+.DS
+rgid = getgid();
+result gid_t rgid;
+
+egid = getegid();
+result gid_t egid;
+.DE
+The access group id set is returned by a \fIgetgroups\fP call*:
+.DS
+ngroups = getgroups(gidsetsize, gidset);
+result int ngroups; int gidsetsize; result int gidset[gidsetsize];
+.DE
+.FS
+* The type of the gidset array in getgroups and setgroups
+remains integer for compatibility with 4.2BSD.
+It may change to \fBgid_t\fP in future releases.
+.FE
+.PP
+The user and group id's
+are assigned at login time using the \fIsetreuid\fP, \fIsetregid\fP,
+and \fIsetgroups\fP calls:
+.DS
+setreuid(ruid, euid);
+int ruid, euid;
+
+setregid(rgid, egid);
+int rgid, egid;
+
+setgroups(gidsetsize, gidset)
+int gidsetsize; int gidset[gidsetsize];
+.DE
+The \fIsetreuid\fP call sets both the real and effective user-id's,
+while the \fIsetregid\fP call sets both the real
+and effective accounting group id's.
+Unless the caller is the super-user, \fIruid\fP
+must be equal to either the current real or effective user-id,
+and \fIrgid\fP equal to either the current real or effective
+accounting group id.  The \fIsetgroups\fP call is restricted
+to the super-user.
+.NH 3
+Process groups
+.PP
+Each process in the system is also normally associated with a \fIprocess
+group\fP.  The group of processes in a process group is sometimes
+referred to as a \fIjob\fP and manipulated by high-level system
+software (such as the shell).
+The current process group of a process is returned by the
+\fIgetpgrp\fP call:
+.DS
+pgrp = getpgrp(pid);
+result int pgrp; int pid;
+.DE
+When a process is in a specific process group it may receive
+software interrupts affecting the group, causing the group to
+suspend or resume execution or to be interrupted or terminated.
+In particular, a system terminal has a process group and only processes
+which are in the process group of the terminal may read from the
+terminal, allowing arbitration of terminals among several different jobs.
+.PP
+The process group associated with a process may be changed by
+the \fIsetpgrp\fP call:
+.DS
+setpgrp(pid, pgrp);
+int pid, pgrp;
+.DE
+Newly created processes are assigned process id's distinct from all
+processes and process groups, and the same process group as their
+parent.  A normal (unprivileged) process may set its process group equal
+to its process id.  A privileged process may set the process group of any
+process to any value.