1 :mod:`resource` --- Resource usage information 2 ============================================== 3 4 .. module:: resource 5 :platform: Unix 6 :synopsis: An interface to provide resource usage information on the current process. 7 8 .. moduleauthor:: Jeremy Hylton <jeremy (a] alum.mit.edu> 9 .. sectionauthor:: Jeremy Hylton <jeremy (a] alum.mit.edu> 10 11 -------------- 12 13 This module provides basic mechanisms for measuring and controlling system 14 resources utilized by a program. 15 16 Symbolic constants are used to specify particular system resources and to 17 request usage information about either the current process or its children. 18 19 An :exc:`OSError` is raised on syscall failure. 20 21 22 .. exception:: error 23 24 A deprecated alias of :exc:`OSError`. 25 26 .. versionchanged:: 3.3 27 Following :pep:`3151`, this class was made an alias of :exc:`OSError`. 28 29 30 Resource Limits 31 --------------- 32 33 Resources usage can be limited using the :func:`setrlimit` function described 34 below. Each resource is controlled by a pair of limits: a soft limit and a hard 35 limit. The soft limit is the current limit, and may be lowered or raised by a 36 process over time. The soft limit can never exceed the hard limit. The hard 37 limit can be lowered to any value greater than the soft limit, but not raised. 38 (Only processes with the effective UID of the super-user can raise a hard 39 limit.) 40 41 The specific resources that can be limited are system dependent. They are 42 described in the :manpage:`getrlimit(2)` man page. The resources listed below 43 are supported when the underlying operating system supports them; resources 44 which cannot be checked or controlled by the operating system are not defined in 45 this module for those platforms. 46 47 48 .. data:: RLIM_INFINITY 49 50 Constant used to represent the limit for an unlimited resource. 51 52 53 .. function:: getrlimit(resource) 54 55 Returns a tuple ``(soft, hard)`` with the current soft and hard limits of 56 *resource*. Raises :exc:`ValueError` if an invalid resource is specified, or 57 :exc:`error` if the underlying system call fails unexpectedly. 58 59 60 .. function:: setrlimit(resource, limits) 61 62 Sets new limits of consumption of *resource*. The *limits* argument must be a 63 tuple ``(soft, hard)`` of two integers describing the new limits. A value of 64 :data:`~resource.RLIM_INFINITY` can be used to request a limit that is 65 unlimited. 66 67 Raises :exc:`ValueError` if an invalid resource is specified, if the new soft 68 limit exceeds the hard limit, or if a process tries to raise its hard limit. 69 Specifying a limit of :data:`~resource.RLIM_INFINITY` when the hard or 70 system limit for that resource is not unlimited will result in a 71 :exc:`ValueError`. A process with the effective UID of super-user can 72 request any valid limit value, including unlimited, but :exc:`ValueError` 73 will still be raised if the requested limit exceeds the system imposed 74 limit. 75 76 ``setrlimit`` may also raise :exc:`error` if the underlying system call 77 fails. 78 79 .. function:: prlimit(pid, resource[, limits]) 80 81 Combines :func:`setrlimit` and :func:`getrlimit` in one function and 82 supports to get and set the resources limits of an arbitrary process. If 83 *pid* is 0, then the call applies to the current process. *resource* and 84 *limits* have the same meaning as in :func:`setrlimit`, except that 85 *limits* is optional. 86 87 When *limits* is not given the function returns the *resource* limit of the 88 process *pid*. When *limits* is given the *resource* limit of the process is 89 set and the former resource limit is returned. 90 91 Raises :exc:`ProcessLookupError` when *pid* can't be found and 92 :exc:`PermissionError` when the user doesn't have ``CAP_SYS_RESOURCE`` for 93 the process. 94 95 .. availability:: Linux 2.6.36 or later with glibc 2.13 or later. 96 97 .. versionadded:: 3.4 98 99 100 These symbols define resources whose consumption can be controlled using the 101 :func:`setrlimit` and :func:`getrlimit` functions described below. The values of 102 these symbols are exactly the constants used by C programs. 103 104 The Unix man page for :manpage:`getrlimit(2)` lists the available resources. 105 Note that not all systems use the same symbol or same value to denote the same 106 resource. This module does not attempt to mask platform differences --- symbols 107 not defined for a platform will not be available from this module on that 108 platform. 109 110 111 .. data:: RLIMIT_CORE 112 113 The maximum size (in bytes) of a core file that the current process can create. 114 This may result in the creation of a partial core file if a larger core would be 115 required to contain the entire process image. 116 117 118 .. data:: RLIMIT_CPU 119 120 The maximum amount of processor time (in seconds) that a process can use. If 121 this limit is exceeded, a :const:`SIGXCPU` signal is sent to the process. (See 122 the :mod:`signal` module documentation for information about how to catch this 123 signal and do something useful, e.g. flush open files to disk.) 124 125 126 .. data:: RLIMIT_FSIZE 127 128 The maximum size of a file which the process may create. 129 130 131 .. data:: RLIMIT_DATA 132 133 The maximum size (in bytes) of the process's heap. 134 135 136 .. data:: RLIMIT_STACK 137 138 The maximum size (in bytes) of the call stack for the current process. This only 139 affects the stack of the main thread in a multi-threaded process. 140 141 142 .. data:: RLIMIT_RSS 143 144 The maximum resident set size that should be made available to the process. 145 146 147 .. data:: RLIMIT_NPROC 148 149 The maximum number of processes the current process may create. 150 151 152 .. data:: RLIMIT_NOFILE 153 154 The maximum number of open file descriptors for the current process. 155 156 157 .. data:: RLIMIT_OFILE 158 159 The BSD name for :const:`RLIMIT_NOFILE`. 160 161 162 .. data:: RLIMIT_MEMLOCK 163 164 The maximum address space which may be locked in memory. 165 166 167 .. data:: RLIMIT_VMEM 168 169 The largest area of mapped memory which the process may occupy. 170 171 172 .. data:: RLIMIT_AS 173 174 The maximum area (in bytes) of address space which may be taken by the process. 175 176 177 .. data:: RLIMIT_MSGQUEUE 178 179 The number of bytes that can be allocated for POSIX message queues. 180 181 .. availability:: Linux 2.6.8 or later. 182 183 .. versionadded:: 3.4 184 185 186 .. data:: RLIMIT_NICE 187 188 The ceiling for the process's nice level (calculated as 20 - rlim_cur). 189 190 .. availability:: Linux 2.6.12 or later. 191 192 .. versionadded:: 3.4 193 194 195 .. data:: RLIMIT_RTPRIO 196 197 The ceiling of the real-time priority. 198 199 .. availability:: Linux 2.6.12 or later. 200 201 .. versionadded:: 3.4 202 203 204 .. data:: RLIMIT_RTTIME 205 206 The time limit (in microseconds) on CPU time that a process can spend 207 under real-time scheduling without making a blocking syscall. 208 209 .. availability:: Linux 2.6.25 or later. 210 211 .. versionadded:: 3.4 212 213 214 .. data:: RLIMIT_SIGPENDING 215 216 The number of signals which the process may queue. 217 218 .. availability:: Linux 2.6.8 or later. 219 220 .. versionadded:: 3.4 221 222 .. data:: RLIMIT_SBSIZE 223 224 The maximum size (in bytes) of socket buffer usage for this user. 225 This limits the amount of network memory, and hence the amount of mbufs, 226 that this user may hold at any time. 227 228 .. availability:: FreeBSD 9 or later. 229 230 .. versionadded:: 3.4 231 232 .. data:: RLIMIT_SWAP 233 234 The maximum size (in bytes) of the swap space that may be reserved or 235 used by all of this user id's processes. 236 This limit is enforced only if bit 1 of the vm.overcommit sysctl is set. 237 Please see :manpage:`tuning(7)` for a complete description of this sysctl. 238 239 .. availability:: FreeBSD 9 or later. 240 241 .. versionadded:: 3.4 242 243 .. data:: RLIMIT_NPTS 244 245 The maximum number of pseudo-terminals created by this user id. 246 247 .. availability:: FreeBSD 9 or later. 248 249 .. versionadded:: 3.4 250 251 Resource Usage 252 -------------- 253 254 These functions are used to retrieve resource usage information: 255 256 257 .. function:: getrusage(who) 258 259 This function returns an object that describes the resources consumed by either 260 the current process or its children, as specified by the *who* parameter. The 261 *who* parameter should be specified using one of the :const:`RUSAGE_\*` 262 constants described below. 263 264 The fields of the return value each describe how a particular system resource 265 has been used, e.g. amount of time spent running is user mode or number of times 266 the process was swapped out of main memory. Some values are dependent on the 267 clock tick internal, e.g. the amount of memory the process is using. 268 269 For backward compatibility, the return value is also accessible as a tuple of 16 270 elements. 271 272 The fields :attr:`ru_utime` and :attr:`ru_stime` of the return value are 273 floating point values representing the amount of time spent executing in user 274 mode and the amount of time spent executing in system mode, respectively. The 275 remaining values are integers. Consult the :manpage:`getrusage(2)` man page for 276 detailed information about these values. A brief summary is presented here: 277 278 +--------+---------------------+-------------------------------+ 279 | Index | Field | Resource | 280 +========+=====================+===============================+ 281 | ``0`` | :attr:`ru_utime` | time in user mode (float) | 282 +--------+---------------------+-------------------------------+ 283 | ``1`` | :attr:`ru_stime` | time in system mode (float) | 284 +--------+---------------------+-------------------------------+ 285 | ``2`` | :attr:`ru_maxrss` | maximum resident set size | 286 +--------+---------------------+-------------------------------+ 287 | ``3`` | :attr:`ru_ixrss` | shared memory size | 288 +--------+---------------------+-------------------------------+ 289 | ``4`` | :attr:`ru_idrss` | unshared memory size | 290 +--------+---------------------+-------------------------------+ 291 | ``5`` | :attr:`ru_isrss` | unshared stack size | 292 +--------+---------------------+-------------------------------+ 293 | ``6`` | :attr:`ru_minflt` | page faults not requiring I/O | 294 +--------+---------------------+-------------------------------+ 295 | ``7`` | :attr:`ru_majflt` | page faults requiring I/O | 296 +--------+---------------------+-------------------------------+ 297 | ``8`` | :attr:`ru_nswap` | number of swap outs | 298 +--------+---------------------+-------------------------------+ 299 | ``9`` | :attr:`ru_inblock` | block input operations | 300 +--------+---------------------+-------------------------------+ 301 | ``10`` | :attr:`ru_oublock` | block output operations | 302 +--------+---------------------+-------------------------------+ 303 | ``11`` | :attr:`ru_msgsnd` | messages sent | 304 +--------+---------------------+-------------------------------+ 305 | ``12`` | :attr:`ru_msgrcv` | messages received | 306 +--------+---------------------+-------------------------------+ 307 | ``13`` | :attr:`ru_nsignals` | signals received | 308 +--------+---------------------+-------------------------------+ 309 | ``14`` | :attr:`ru_nvcsw` | voluntary context switches | 310 +--------+---------------------+-------------------------------+ 311 | ``15`` | :attr:`ru_nivcsw` | involuntary context switches | 312 +--------+---------------------+-------------------------------+ 313 314 This function will raise a :exc:`ValueError` if an invalid *who* parameter is 315 specified. It may also raise :exc:`error` exception in unusual circumstances. 316 317 318 .. function:: getpagesize() 319 320 Returns the number of bytes in a system page. (This need not be the same as the 321 hardware page size.) 322 323 The following :const:`RUSAGE_\*` symbols are passed to the :func:`getrusage` 324 function to specify which processes information should be provided for. 325 326 327 .. data:: RUSAGE_SELF 328 329 Pass to :func:`getrusage` to request resources consumed by the calling 330 process, which is the sum of resources used by all threads in the process. 331 332 333 .. data:: RUSAGE_CHILDREN 334 335 Pass to :func:`getrusage` to request resources consumed by child processes 336 of the calling process which have been terminated and waited for. 337 338 339 .. data:: RUSAGE_BOTH 340 341 Pass to :func:`getrusage` to request resources consumed by both the current 342 process and child processes. May not be available on all systems. 343 344 345 .. data:: RUSAGE_THREAD 346 347 Pass to :func:`getrusage` to request resources consumed by the current 348 thread. May not be available on all systems. 349 350 .. versionadded:: 3.2 351
