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1.1 root 1: .\" Copyright (c) 1983 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)1.1.t 6.2 (Berkeley) 5/12/86
6: .\"
7: .sh "Processes and protection
8: .NH 3
9: Host and process identifiers
10: .PP
11: Each UNIX host has associated with it a 32-bit host id, and a host
12: name of up to 64 characters (as defined by MAXHOSTNAMELEN in
13: \fI<sys/param.h>\fP).
14: These are set (by a privileged user)
15: and returned by the calls:
16: .DS
17: sethostid(hostid)
18: long hostid;
19:
20: hostid = gethostid();
21: result long hostid;
22:
23: sethostname(name, len)
24: char *name; int len;
25:
26: len = gethostname(buf, buflen)
27: result int len; result char *buf; int buflen;
28: .DE
29: On each host runs a set of \fIprocesses\fP.
30: Each process is largely independent of other processes,
31: having its own protection domain, address space, timers, and
32: an independent set of references to system or user implemented objects.
33: .PP
34: Each process in a host is named by an integer
35: called the \fIprocess id\fP. This number is
36: in the range 1-30000
37: and is returned by
38: the \fIgetpid\fP routine:
39: .DS
40: pid = getpid();
41: result int pid;
42: .DE
43: On each UNIX host this identifier is guaranteed to be unique;
44: in a multi-host environment, the (hostid, process id) pairs are
45: guaranteed unique.
46: .NH 3
47: Process creation and termination
48: .PP
49: A new process is created by making a logical duplicate of an
50: existing process:
51: .DS
52: pid = fork();
53: result int pid;
54: .DE
55: The \fIfork\fP call returns twice, once in the parent process, where
56: \fIpid\fP is the process identifier of the child,
57: and once in the child process where \fIpid\fP is 0.
58: The parent-child relationship induces a hierarchical structure on
59: the set of processes in the system.
60: .PP
61: A process may terminate by executing an \fIexit\fP call:
62: .DS
63: exit(status)
64: int status;
65: .DE
66: returning 8 bits of exit status to its parent.
67: .PP
68: When a child process exits or
69: terminates abnormally, the parent process receives
70: information about any
71: event which caused termination of the child process. A
72: second call provides a non-blocking interface and may also be used
73: to retrieve information about resources consumed by the process during its
74: lifetime.
75: .DS
76: #include <sys/wait.h>
77:
78: pid = wait(astatus);
79: result int pid; result union wait *astatus;
80:
81: pid = wait3(astatus, options, arusage);
82: result int pid; result union waitstatus *astatus;
83: int options; result struct rusage *arusage;
84: .DE
85: .PP
86: A process can overlay itself with the memory image of another process,
87: passing the newly created process a set of parameters, using the call:
88: .DS
89: execve(name, argv, envp)
90: char *name, **argv, **envp;
91: .DE
92: The specified \fIname\fP must be a file which is in a format recognized
93: by the system, either a binary executable file or a file which causes
94: the execution of a specified interpreter program to process its contents.
95: .NH 3
96: User and group ids
97: .PP
98: Each process in the system has associated with it two user-id's:
99: a \fIreal user id\fP and a \fIeffective user id\fP, both 16 bit
100: unsigned integers (type \fBuid_t\fP).
101: Each process has an \fIreal accounting group id\fP and an \fIeffective
102: accounting group id\fP and a set of
103: \fIaccess group id's\fP. The group id's are 16 bit unsigned integers
104: (type \fBgid_t\fP).
105: Each process may be in several different access groups, with the maximum
106: concurrent number of access groups a system compilation parameter,
107: the constant NGROUPS in the file \fI<sys/param.h>\fP,
108: guaranteed to be at least 8.
109: .PP
110: The real and effective user ids associated with a process are returned by:
111: .DS
112: ruid = getuid();
113: result uid_t ruid;
114:
115: euid = geteuid();
116: result uid_t euid;
117: .DE
118: the real and effective accounting group ids by:
119: .DS
120: rgid = getgid();
121: result gid_t rgid;
122:
123: egid = getegid();
124: result gid_t egid;
125: .DE
126: The access group id set is returned by a \fIgetgroups\fP call*:
127: .DS
128: ngroups = getgroups(gidsetsize, gidset);
129: result int ngroups; int gidsetsize; result int gidset[gidsetsize];
130: .DE
131: .FS
132: * The type of the gidset array in getgroups and setgroups
133: remains integer for compatibility with 4.2BSD.
134: It may change to \fBgid_t\fP in future releases.
135: .FE
136: .PP
137: The user and group id's
138: are assigned at login time using the \fIsetreuid\fP, \fIsetregid\fP,
139: and \fIsetgroups\fP calls:
140: .DS
141: setreuid(ruid, euid);
142: int ruid, euid;
143:
144: setregid(rgid, egid);
145: int rgid, egid;
146:
147: setgroups(gidsetsize, gidset)
148: int gidsetsize; int gidset[gidsetsize];
149: .DE
150: The \fIsetreuid\fP call sets both the real and effective user-id's,
151: while the \fIsetregid\fP call sets both the real
152: and effective accounting group id's.
153: Unless the caller is the super-user, \fIruid\fP
154: must be equal to either the current real or effective user-id,
155: and \fIrgid\fP equal to either the current real or effective
156: accounting group id. The \fIsetgroups\fP call is restricted
157: to the super-user.
158: .NH 3
159: Process groups
160: .PP
161: Each process in the system is also normally associated with a \fIprocess
162: group\fP. The group of processes in a process group is sometimes
163: referred to as a \fIjob\fP and manipulated by high-level system
164: software (such as the shell).
165: The current process group of a process is returned by the
166: \fIgetpgrp\fP call:
167: .DS
168: pgrp = getpgrp(pid);
169: result int pgrp; int pid;
170: .DE
171: When a process is in a specific process group it may receive
172: software interrupts affecting the group, causing the group to
173: suspend or resume execution or to be interrupted or terminated.
174: In particular, a system terminal has a process group and only processes
175: which are in the process group of the terminal may read from the
176: terminal, allowing arbitration of terminals among several different jobs.
177: .PP
178: The process group associated with a process may be changed by
179: the \fIsetpgrp\fP call:
180: .DS
181: setpgrp(pid, pgrp);
182: int pid, pgrp;
183: .DE
184: Newly created processes are assigned process id's distinct from all
185: processes and process groups, and the same process group as their
186: parent. A normal (unprivileged) process may set its process group equal
187: to its process id. A privileged process may set the process group of any
188: process to any value.
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