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