1.\"	$NetBSD: getrlimit.2,v 1.36 2012/06/09 02:36:25 christos Exp $
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30.\"     @(#)getrlimit.2	8.1 (Berkeley) 6/4/93
31.\"
32.Dd June 8, 2012
33.Dt GETRLIMIT 2
34.Os
35.Sh NAME
36.Nm getrlimit ,
37.Nm setrlimit
38.Nd control maximum system resource consumption
39.Sh LIBRARY
40.Lb libc
41.Sh SYNOPSIS
42.In sys/resource.h
43.Ft int
44.Fn getrlimit "int resource" "struct rlimit *rlp"
45.Ft int
46.Fn setrlimit "int resource" "const struct rlimit *rlp"
47.Sh DESCRIPTION
48Limits on the consumption of system resources by the current process
49and each process it creates may be obtained with the
50.Fn getrlimit
51call, and set with the
52.Fn setrlimit
53call.
54Resources of an arbitrary process can be obtained/changed using
55.Xr sysctl 3 .
56.Pp
57The
58.Fa resource
59parameter is one of the following:
60.Bl -tag -width RLIMIT_FSIZEAA
61.It Li RLIMIT_AS
62The maximum amount (in bytes) of virtual memory the process is allowed to map.
63.It Li RLIMIT_CORE
64The largest size (in bytes)
65.Pa core
66file that may be created.
67.It Li RLIMIT_CPU
68The maximum amount of CPU time (in seconds) to be used by
69each process.
70.It Li RLIMIT_DATA
71The maximum size (in bytes) of the data segment for a process;
72this defines how far a program may extend its break with the
73.Xr sbrk 2
74system call.
75.It Li RLIMIT_FSIZE
76The largest size (in bytes) file that may be created.
77.It Li RLIMIT_MEMLOCK
78The maximum size (in bytes) which a process may lock into memory
79using the
80.Xr mlock 2
81function.
82.It Li RLIMIT_NOFILE
83The maximum number of open files for this process.
84.It Li RLIMIT_NPROC
85The maximum number of simultaneous processes for this user id.
86.It Li RLIMIT_NTHR
87The maximum number of simultaneous threads (Lightweight Processes) for this
88user id.
89Kernel threads and the first thread of each process are not counted against
90this limit.
91.It Li RLIMIT_RSS
92The maximum size (in bytes) to which a process's resident set size may
93grow.
94This imposes a limit on the amount of physical memory to be given to
95a process; if memory is tight, the system will prefer to take memory
96from processes that are exceeding their declared resident set size.
97.It Li RLIMIT_SBSIZE
98The maximum size (in bytes) of the socket buffers
99set by the
100.Xr setsockopt 2
101.Dv SO_RCVBUF
102and
103.Dv SO_SNDBUF
104options.
105.It Li RLIMIT_STACK
106The maximum size (in bytes) of the stack segment for a process;
107this defines how far a program's stack segment may be extended.
108Stack extension is performed automatically by the system.
109.El
110.Pp
111A resource limit is specified as a soft limit and a hard limit.
112When a soft limit is exceeded a process may receive a signal (for example,
113if the CPU time or file size is exceeded), but it will be allowed to
114continue execution until it reaches the hard limit (or modifies
115its resource limit).
116The
117.Em rlimit
118structure is used to specify the hard and soft limits on a resource,
119.Bd -literal -offset indent
120struct rlimit {
121	rlim_t	rlim_cur;	/* current (soft) limit */
122	rlim_t	rlim_max;	/* hard limit */
123};
124.Ed
125.Pp
126Only the super-user may raise the maximum limits.
127Other users may only alter
128.Fa rlim_cur
129within the range from 0 to
130.Fa rlim_max
131or (irreversibly) lower
132.Fa rlim_max .
133.Pp
134An
135.Dq infinite
136value for a limit is defined as
137.Dv RLIM_INFINITY .
138.Pp
139Because this information is stored in the per-process information,
140this system call must be executed directly by the shell if it
141is to affect all future processes created by the shell.
142Thus, shells provide built-in commands to change the limits
143.Ic ( limit
144for
145.Xr csh 1 ,
146or
147.Ic ulimit
148for
149.Xr sh 1 ) .
150.Pp
151The system refuses to extend the data or stack space when the limits
152would be exceeded in the normal way: a
153.Xr brk 2
154call fails if the data space limit is reached.
155When the stack limit is reached, the process receives
156a segmentation fault
157.Pq Dv SIGSEGV ;
158if this signal is not
159caught by a handler using the signal stack, this signal
160will kill the process.
161.Pp
162A file I/O operation that would create a file larger that the process'
163soft limit will cause the write to fail and a signal
164.Dv SIGXFSZ
165to be
166generated; this normally terminates the process, but may be caught.
167When the soft CPU time limit is exceeded, a signal
168.Dv SIGXCPU
169is sent to the
170offending process.
171.Sh RETURN VALUES
172A 0 return value indicates that the call succeeded, changing
173or returning the resource limit.
174Otherwise, \-1 is returned and the global variable
175.Va errno
176is set to indicate the error.
177.Sh ERRORS
178The
179.Fn getrlimit
180and
181.Fn setrlimit
182will fail if:
183.Bl -tag -width Er
184.It Bq Er EFAULT
185The address specified for
186.Fa rlp
187is invalid.
188.It Bq Er EINVAL
189Specified
190.Fa resource
191was invalid; or, in the
192.Fn setrlimit
193call, the specified
194.Fa rlim_cur
195exceeds the specified
196.Fa rlim_max .
197.It Bq Er EPERM
198The limit specified to
199.Fn setrlimit
200would have
201raised the maximum limit value, and the caller is not the super-user.
202.El
203.Pp
204The
205.Fn setrlimit
206function may fail if:
207.Bl -tag -width Er
208.It Bq Er EINVAL
209The limit specified to
210.Fn setrlimit
211cannot be lowered, because current usage is already higher than the limit.
212.El
213.Sh SEE ALSO
214.Xr csh 1 ,
215.Xr sh 1 ,
216.Xr mlock 2 ,
217.Xr setsockopt 2 ,
218.Xr sigaction 2 ,
219.Xr sigaltstack 2 ,
220.Xr libquota 3 ,
221.Xr sysctl 3
222.\" Sh STANDARDS
223.\" With exception of
224.\" .Li RLIMIT_AS
225.\" (which is not currently supported), the
226.\" .Fn getrlimit
227.\" and
228.\" .Fn setrlimit
229.\" functions conform to
230.\" .St -susv2 .
231.Sh HISTORY
232The
233.Fn getrlimit
234function call appeared in
235.Bx 4.2 .
236.Sh BUGS
237The resource limit
238.Dv RLIMIT_RSS
239is not implemented in
240.Xr uvm 9
241which means that process memory size limits are not enforced.
242