xref: /dragonfly/lib/libc/sys/getrlimit.2 (revision cecb9aae) 
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32.\"     @(#)getrlimit.2	8.1 (Berkeley) 6/4/93
33.\" $FreeBSD: src/lib/libc/sys/getrlimit.2,v 1.10.2.5 2001/12/14 18:34:00 ru Exp $
34.\"
35.Dd July 6, 2009
36.Dt GETRLIMIT 2
37.Os
38.Sh NAME
39.Nm getrlimit ,
40.Nm setrlimit
41.Nd control maximum system resource consumption
42.Sh LIBRARY
43.Lb libc
44.Sh SYNOPSIS
45.In sys/types.h
46.In sys/time.h
47.In sys/resource.h
48.Ft int
49.Fn getrlimit "int resource" "struct rlimit *rlp"
50.Ft int
51.Fn setrlimit "int resource" "const struct rlimit *rlp"
52.Sh DESCRIPTION
53Limits on the consumption of system resources by the current process
54and each process it creates may be obtained with the
55.Fn getrlimit
56call, and set with the
57.Fn setrlimit
58call.
59.Pp
60The
61.Fa resource
62parameter is one of the following:
63.Bl -tag -width RLIMIT_FSIZEAA
64.It Li RLIMIT_AS
65The maximum size (in bytes) of a process' total available memory.
66If this limit is exceeded, the
67.Xr malloc 3
68and
69.Xr mmap 2
70functions will fail and
71.Va errno
72set to
73.Er ENOMEM .
74Moreover, the automatic stack growth will fail as well.
75.It Li RLIMIT_CORE
76The largest size (in bytes)
77.Xr core 5
78file that may be created.
79.It Li RLIMIT_CPU
80The maximum amount of cpu time (in seconds) to be used by
81each process.
82.It Li RLIMIT_DATA
83The maximum size (in bytes) of the data segment for a process;
84this defines how far a program may extend its break with the
85.Xr sbrk 2
86system call.
87.It Li RLIMIT_FSIZE
88The largest size (in bytes) file that may be created.
89.It Li RLIMIT_MEMLOCK
90The maximum size (in bytes) which a process may lock into memory
91using the
92.Xr mlock 2
93function.
94.It Li RLIMIT_NOFILE
95The maximum number of open files for this process.
96.It Li RLIMIT_NPROC
97The maximum number of simultaneous processes for this user id.
98.It Li RLIMIT_RSS
99The maximum size (in bytes) to which a process's resident set size may
100grow.
101This imposes a limit on the amount of physical memory to be given to
102a process; if memory is tight, the system will prefer to take memory
103from processes that are exceeding their declared resident set size.
104.It Li RLIMIT_STACK
105The maximum size (in bytes) of the stack segment for a process;
106this defines how far a program's stack segment may be extended.
107Stack extension is performed automatically by the system.
108.It Li RLIMIT_SBSIZE
109The maximum size (in bytes) of socket buffer usage for this user.
110This limits the amount of network memory, and hence the amount of
111mbufs, that this user may hold at any time.
112.It Li RLIMIT_POSIXLOCK
113The maximum number of POSIX-type advisory-mode locks available to
114this user.
115.El
116.Pp
117A resource limit is specified as a soft limit and a hard limit.
118When a soft limit is exceeded a process may receive a signal (for example, if
119the cpu time or file size is exceeded), but it will be allowed to
120continue execution until it reaches the hard limit (or modifies
121its resource limit).
122The
123.Em rlimit
124structure is used to specify the hard and soft limits on a resource,
125.Bd -literal -offset indent
126struct rlimit {
127	rlim_t	rlim_cur;	/* current (soft) limit */
128	rlim_t	rlim_max;	/* maximum value for rlim_cur */
129};
130.Ed
131.Pp
132Only the super-user may raise the maximum limits.
133Other users may only alter
134.Fa rlim_cur
135within the range from 0 to
136.Fa rlim_max
137or (irreversibly) lower
138.Fa rlim_max .
139.Pp
140An
141.Dq infinite
142value for a limit is defined as
143.Dv RLIM_INFINITY .
144.Pp
145Because this information is stored in the per-process information,
146this system call must be executed directly by the shell if it
147is to affect all future processes created by the shell;
148.Ic limit
149is thus a built-in command to
150.Xr csh 1 .
151.Pp
152The system refuses to extend the data or stack space when the limits
153would be exceeded in the normal way: a
154.Xr brk 2
155call fails if the data space limit is reached.
156When the stack limit is reached, the process receives
157a segmentation fault
158.Pq Dv SIGSEGV ;
159if this signal is not
160caught by a handler using the signal stack, this signal
161will kill the process.
162.Pp
163A file I/O operation that would create a file larger than the process'
164soft limit will cause the write to fail and a signal
165.Dv SIGXFSZ
166to be
167generated; this normally terminates the process, but may be caught.
168When the soft cpu time limit is exceeded, a signal
169.Dv SIGXCPU
170is sent to the
171offending process.
172.Sh RETURN VALUES
173.Rv -std
174.Sh ERRORS
175.Fn Getrlimit
176and
177.Fn setrlimit
178will fail if:
179.Bl -tag -width Er
180.It Bq Er EFAULT
181The address specified for
182.Fa rlp
183is invalid.
184.It Bq Er EPERM
185The limit specified to
186.Fn setrlimit
187would have
188raised the maximum limit value, and the caller is not the super-user.
189.El
190.Sh SEE ALSO
191.Xr csh 1 ,
192.Xr quota 1 ,
193.Xr quotactl 2 ,
194.Xr sigaction 2 ,
195.Xr sigaltstack 2 ,
196.Xr sysctl 3 ,
197.Xr ulimit 3
198.Sh HISTORY
199The
200.Fn getrlimit
201function call appeared in
202.Bx 4.2 .
203