35.11.1. Resource Limits¶

Resources usage can be limited using thesetrlimit() function describedbelow. Each resource is controlled by a pair of limits: a soft limit and a hardlimit. The soft limit is the current limit, and may be lowered or raised by aprocess over time. The soft limit can never exceed the hard limit. The hardlimit can be lowered to any value greater than the soft limit, but not raised.(Only processes with the effective UID of the super-user can raise a hardlimit.)

The specific resources that can be limited are system dependent. They aredescribed in thegetrlimit(2) man page. The resources listed beloware supported when the underlying operating system supports them; resourceswhich cannot be checked or controlled by the operating system are not defined inthis module for those platforms.

resource.RLIM_INFINITY¶

Constant used to represent the limit for an unlimited resource.

resource.getrlimit(resource)¶

Returns a tuple(soft,hard) with the current soft and hard limits ofresource. RaisesValueError if an invalid resource is specified, orerror if the underlying system call fails unexpectedly.

resource.setrlimit(resource,limits)¶

Sets new limits of consumption ofresource. Thelimits argument must be atuple(soft,hard) of two integers describing the new limits. A value ofRLIM_INFINITY can be used to request a limit that isunlimited.

RaisesValueError if an invalid resource is specified, if the new softlimit exceeds the hard limit, or if a process tries to raise its hard limit.Specifying a limit ofRLIM_INFINITY when the hard orsystem limit for that resource is not unlimited will result in aValueError. A process with the effective UID of super-user canrequest any valid limit value, including unlimited, butValueErrorwill still be raised if the requested limit exceeds the system imposedlimit.

setrlimit may also raiseerror if the underlying system callfails.

resource.prlimit(pid,resource[,limits])¶

Combinessetrlimit() andgetrlimit() in one function andsupports to get and set the resources limits of an arbitrary process. Ifpid is 0, then the call applies to the current process.resource andlimits have the same meaning as insetrlimit(), except thatlimits is optional.

Whenlimits is not given the function returns theresource limit of theprocesspid. Whenlimits is given theresource limit of the process isset and the former resource limit is returned.

RaisesProcessLookupError whenpid can’t be found andPermissionError when the user doesn’t haveCAP_SYS_RESOURCE forthe process.

Availability: Linux 2.6.36 or later with glibc 2.13 or later

New in version 3.4.

These symbols define resources whose consumption can be controlled using thesetrlimit() andgetrlimit() functions described below. The values ofthese symbols are exactly the constants used by C programs.

The Unix man page forgetrlimit(2) lists the available resources.Note that not all systems use the same symbol or same value to denote the sameresource. This module does not attempt to mask platform differences — symbolsnot defined for a platform will not be available from this module on thatplatform.

resource.RLIMIT_CORE¶

The maximum size (in bytes) of a core file that the current process can create.This may result in the creation of a partial core file if a larger core would berequired to contain the entire process image.

resource.RLIMIT_CPU¶

The maximum amount of processor time (in seconds) that a process can use. Ifthis limit is exceeded, aSIGXCPU signal is sent to the process. (Seethesignal module documentation for information about how to catch thissignal and do something useful, e.g. flush open files to disk.)

resource.RLIMIT_FSIZE¶

The maximum size of a file which the process may create.

resource.RLIMIT_DATA¶

The maximum size (in bytes) of the process’s heap.

resource.RLIMIT_STACK¶

The maximum size (in bytes) of the call stack for the current process. This onlyaffects the stack of the main thread in a multi-threaded process.

resource.RLIMIT_RSS¶

The maximum resident set size that should be made available to the process.

resource.RLIMIT_NPROC¶

The maximum number of processes the current process may create.

resource.RLIMIT_NOFILE¶

The maximum number of open file descriptors for the current process.

resource.RLIMIT_OFILE¶

The BSD name forRLIMIT_NOFILE.

resource.RLIMIT_MEMLOCK¶

The maximum address space which may be locked in memory.

resource.RLIMIT_VMEM¶

The largest area of mapped memory which the process may occupy.

resource.RLIMIT_AS¶

The maximum area (in bytes) of address space which may be taken by the process.

resource.RLIMIT_MSGQUEUE¶

The number of bytes that can be allocated for POSIX message queues.

Availability: Linux 2.6.8 or later.

New in version 3.4.

resource.RLIMIT_NICE¶

The ceiling for the process’s nice level (calculated as 20 - rlim_cur).

Availability: Linux 2.6.12 or later.

New in version 3.4.

resource.RLIMIT_RTPRIO¶

The ceiling of the real-time priority.

Availability: Linux 2.6.12 or later.

New in version 3.4.

resource.RLIMIT_RTTIME¶

The time limit (in microseconds) on CPU time that a process can spendunder real-time scheduling without making a blocking syscall.

Availability: Linux 2.6.25 or later.

New in version 3.4.

resource.RLIMIT_SIGPENDING¶

The number of signals which the process may queue.

Availability: Linux 2.6.8 or later.

New in version 3.4.

resource.RLIMIT_SBSIZE¶

The maximum size (in bytes) of socket buffer usage for this user.This limits the amount of network memory, and hence the amount of mbufs,that this user may hold at any time.

Availability: FreeBSD 9 or later.

New in version 3.4.

resource.RLIMIT_SWAP¶

The maximum size (in bytes) of the swap space that may be reserved orused by all of this user id’s processes.This limit is enforced only if bit 1 of the vm.overcommit sysctl is set.Please seetuning(7) for a complete description of this sysctl.

Availability: FreeBSD 9 or later.

New in version 3.4.

resource.RLIMIT_NPTS¶

The maximum number of pseudo-terminals created by this user id.

Availability: FreeBSD 9 or later.

New in version 3.4.

35.11.2. Resource Usage¶

These functions are used to retrieve resource usage information:

resource.getrusage(who)¶

This function returns an object that describes the resources consumed by eitherthe current process or its children, as specified by thewho parameter. Thewho parameter should be specified using one of theRUSAGE_*constants described below.

The fields of the return value each describe how a particular system resourcehas been used, e.g. amount of time spent running is user mode or number of timesthe process was swapped out of main memory. Some values are dependent on theclock tick internal, e.g. the amount of memory the process is using.

For backward compatibility, the return value is also accessible as a tuple of 16elements.

The fieldsru_utime andru_stime of the return value arefloating point values representing the amount of time spent executing in usermode and the amount of time spent executing in system mode, respectively. Theremaining values are integers. Consult thegetrusage(2) man page fordetailed information about these values. A brief summary is presented here:

Index	Field	Resource
0	ru_utime	time in user mode (float)
1	ru_stime	time in system mode (float)
2	ru_maxrss	maximum resident set size
3	ru_ixrss	shared memory size
4	ru_idrss	unshared memory size
5	ru_isrss	unshared stack size
6	ru_minflt	page faults not requiring I/O
7	ru_majflt	page faults requiring I/O
8	ru_nswap	number of swap outs
9	ru_inblock	block input operations
10	ru_oublock	block output operations
11	ru_msgsnd	messages sent
12	ru_msgrcv	messages received
13	ru_nsignals	signals received
14	ru_nvcsw	voluntary context switches
15	ru_nivcsw	involuntary context switches

This function will raise aValueError if an invalidwho parameter isspecified. It may also raiseerror exception in unusual circumstances.

resource.getpagesize()¶

Returns the number of bytes in a system page. (This need not be the same as thehardware page size.)

The followingRUSAGE_* symbols are passed to thegetrusage()function to specify which processes information should be provided for.

resource.RUSAGE_SELF¶

Pass togetrusage() to request resources consumed by the callingprocess, which is the sum of resources used by all threads in the process.

resource.RUSAGE_CHILDREN¶

Pass togetrusage() to request resources consumed by child processesof the calling process which have been terminated and waited for.

resource.RUSAGE_BOTH¶

Pass togetrusage() to request resources consumed by both the currentprocess and child processes. May not be available on all systems.

resource.RUSAGE_THREAD¶

Pass togetrusage() to request resources consumed by the currentthread. May not be available on all systems.

New in version 3.2.