bsd/man/man2/getrlimit.2

   1 .\"     $NetBSD: getrlimit.2,v 1.8 1995/10/12 15:40:58 jtc Exp $
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  34 .\"     @(#)getrlimit.2 8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt GETRLIMIT 2
  38 .Os BSD 4
  39 .Sh NAME
  40 .Nm getrlimit ,
  41 .Nm setrlimit
  42 .Nd control maximum system resource consumption
  43 .Sh SYNOPSIS
  44 .Fd #include <sys/resource.h>
  45 .Ft int
  46 .Fo getrlimit
  47 .Fa "int resource"
  48 .Fa "struct rlimit *rlp"
  49 .Fc
  50 .Ft int
  51 .Fo setrlimit
  52 .Fa "int resource"
  53 .Fa "const struct rlimit *rlp"
  54 .Fc
  55 .Sh DESCRIPTION
  56 Limits on the consumption of system resources by the current process
  57 and each process it creates may be obtained with the
  58 .Fn getrlimit
  59 call, and set with the
  60 .Fn setrlimit
  61 call.
  62 .Pp
  63 The
  64 .Fa resource
  65 parameter is one of the following:
  66 .Bl -tag -width RLIMIT_FSIZEAA
  67 .\" ========
  68 .It Li RLIMIT_CORE
  69 The largest size (in bytes)
  70 .Xr core
  71 file that may be created.
  72 .\" ========
  73 .It Li RLIMIT_CPU
  74 The maximum amount of cpu time (in seconds) to be used by
  75 each process.
  76 .\" ========
  77 .It Li RLIMIT_DATA
  78 The maximum size (in bytes) of the data segment for a process;
  79 this defines how far a program may extend its break with the
  80 .Xr sbrk 2
  81 system call.
  82 .\" ========
  83 .It Li RLIMIT_FSIZE
  84 The largest size (in bytes) file that may be created.
  85 .\" ========
  86 .It Li RLIMIT_MEMLOCK
  87 The maximum size (in bytes) which a process may lock into memory
  88 using the
  89 .Xr mlock 2
  90 function.
  91 .\" ========
  92 .It Li RLIMIT_NOFILE
  93 The maximum number of open files for this process.
  94 .\" ========
  95 .It Li RLIMIT_NPROC
  96 The maximum number of simultaneous processes for this user id.
  97 .\" ========
  98 .It Li RLIMIT_RSS
  99 The maximum size (in bytes)
 100 to which a process's resident set size may grow.
 101 This imposes a limit on the amount of physical memory
 102 to be given to a process;
 103 if memory is tight, the system will prefer to take memory
 104 from processes that are exceeding their declared resident set size.
 105 .\" ========
 106 .It Li RLIMIT_STACK
 107 The maximum size (in bytes) of the stack segment for a process;
 108 this defines how far a program's stack segment may be extended.
 109 Stack extension is performed automatically by the system.
 110 .El
 111 .Pp
 112 A resource limit is specified as a soft limit and a hard limit.  When a
 113 soft limit is exceeded a process may receive a signal (for example, if
 114 the cpu time or file size is exceeded), but it will be allowed to
 115 continue execution until it reaches the hard limit (or modifies
 116 its resource limit).  The
 117 .Em rlimit
 118 structure is used to specify the hard and soft limits on a resource,
 119 .Bd -literal -offset indent
 120 struct rlimit {
 121         rlim_t  rlim_cur;       /* current (soft) limit */
 122         rlim_t  rlim_max;       /* hard limit */
 123 };
 124 .Ed
 125 .Pp
 126 Only the super-user may raise the maximum limits.  Other users
 127 may only alter
 128 .Fa rlim_cur
 129 within the range from 0 to
 130 .Fa rlim_max
 131 or (irreversibly) lower
 132 .Fa rlim_max .
 133 .Pp
 134 Because this information is stored in the per-process information,
 135 this system call must be executed directly by the shell if it
 136 is to affect all future processes created by the shell;
 137 .Ic limit
 138 is thus a built-in command to
 139 .Xr csh 1
 140 and
 141 .Ic ulimit
 142 is the
 143 .Xr sh 1
 144 equivalent.
 145 .Pp
 146 The system refuses to extend the data or stack space when the limits
 147 would be exceeded in the normal way: a
 148 .Xr break
 149 call fails if the data space limit is reached.
 150 When the stack limit is reached, the process receives
 151 a segmentation fault
 152 .Pq Dv SIGSEGV ;
 153 if this signal is not
 154 caught by a handler using the signal stack, this signal
 155 will kill the process.
 156 .Pp
 157 A file I/O operation that would create a file larger that the process'
 158 soft limit will cause the write to fail and a signal
 159 .Dv SIGXFSZ
 160 to be
 161 generated; this normally terminates the process, but may be caught.  When
 162 the soft cpu time limit is exceeded, a signal
 163 .Dv SIGXCPU
 164 is sent to the
 165 offending process.
 166 .Sh RETURN VALUES
 167 A 0 return value indicates that the call succeeded, changing
 168 or returning the resource limit.   A return value of -1 indicates
 169 that an error occurred, and an error code is stored in the global
 170 location
 171 .Va errno .
 172 .Sh ERRORS
 173 The
 174 .Fn getrlimit
 175 and
 176 .Fn setrlimit
 177 system calls will fail if:
 178 .Bl -tag -width Er
 179 .\" ==========
 180 .It Bq Er EFAULT
 181 The address specified for
 182 .Fa rlp
 183 is invalid.
 184 .\" ==========
 185 .It Bq Er EINVAL
 186 .Fa resource
 187 is invalid.
 188 .El
 189 .Pp
 190 The
 191 .Fn setrlimit
 192 call will fail if:
 193 .Bl -tag -width Er
 194 .\" ==========
 195 .It Bq Er EINVAL
 196 The specified limit is invalid
 197 (e.g., RLIM_INFINITY or lower than rlim_cur).
 198 .\" ==========
 199 .It Bq Er EPERM
 200 The limit specified would have raised the maximum limit value
 201 and the caller is not the super-user.
 202 .El
 203 .Sh LEGACY SYNOPSIS
 204 .Fd #include <sys/types.h>
 205 .Fd #include <sys/time.h>
 206 .Fd #include <sys/resource.h>
 207 .Pp
 208 The include files
 209 .In sys/types.h
 210 and
 211 .In sys/time.h
 212 are necessary.
 213 .Sh COMPATIBILITY
 214 .Fn setrlimit
 215 now returns with
 216 .Va errno
 217 set to EINVAL in places that historically succeeded.
 218 It no longer accepts "rlim_cur = RLIM_INFINITY" for RLIM_NOFILE.
 219 Use "rlim_cur = min(OPEN_MAX, rlim_max)".
 220 .Sh SEE ALSO
 221 .Xr csh 1 ,
 222 .Xr sh 1 ,
 223 .Xr quota 2 ,
 224 .Xr sigaction 2 ,
 225 .Xr sigaltstack 2 ,
 226 .Xr sysctl 3 ,
 227 .Xr compat 5
 228 .Sh HISTORY
 229 The
 230 .Fn getrlimit
 231 function call appeared in
 232 .Bx 4.2 .