| Python 3.6.5 Documentation > "resource" — Resource usage information
"resource" — Resource usage information
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This module provides basic mechanisms for measuring and controlling
system resources utilized by a program.
Symbolic constants are used to specify particular system resources and
to request usage information about either the current process or its
children.
An "OSError" is raised on syscall failure.
exception resource.error
A deprecated alias of "OSError".
Changed in version 3.3: Following **PEP 3151**, this class was made
an alias of "OSError".
Resource Limits
===============
Resources usage can be limited using the "setrlimit()" function
described below. Each resource is controlled by a pair of limits: a
soft limit and a hard limit. The soft limit is the current limit, and
may be lowered or raised by a process over time. The soft limit can
never exceed the hard limit. The hard limit 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 hard limit.)
The specific resources that can be limited are system dependent. They
are described in the *getrlimit(2)* man page. The resources listed
below are supported when the underlying operating system supports
them; resources which cannot be checked or controlled by the operating
system are not defined in this 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 of *resource*. Raises "ValueError" if an invalid resource is
specified, or "error" if the underlying system call fails
unexpectedly.
resource.setrlimit(resource, limits)
Sets new limits of consumption of *resource*. The *limits* argument
must be a tuple "(soft, hard)" of two integers describing the new
limits. A value of "RLIM_INFINITY" can be used to request a limit
that is unlimited.
Raises "ValueError" if an invalid resource is specified, if the new
soft limit exceeds the hard limit, or if a process tries to raise
its hard limit. Specifying a limit of "RLIM_INFINITY" when the hard
or system limit for that resource is not unlimited will result in a
"ValueError". A process with the effective UID of super-user can
request any valid limit value, including unlimited, but
"ValueError" will still be raised if the requested limit exceeds
the system imposed limit.
"setrlimit" may also raise "error" if the underlying system call
fails.
resource.prlimit(pid, resource[, limits])
Combines "setrlimit()" and "getrlimit()" in one function and
supports to get and set the resources limits of an arbitrary
process. If *pid* is 0, then the call applies to the current
process. *resource* and *limits* have the same meaning as in
"setrlimit()", except that *limits* is optional.
When *limits* is not given the function returns the *resource*
limit of the process *pid*. When *limits* is given the *resource*
limit of the process is set and the former resource limit is
returned.
Raises "ProcessLookupError" when *pid* can’t be found and
"PermissionError" when the user doesn’t have "CAP_SYS_RESOURCE" for
the 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 the "setrlimit()" and "getrlimit()" functions described below.
The values of these symbols are exactly the constants used by C
programs.
The Unix man page for *getrlimit(2)* lists the available resources.
Note that not all systems use the same symbol or same value to denote
the same resource. This module does not attempt to mask platform
differences — symbols not defined for a platform will not be available
from this module on that platform.
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 be required to contain the entire process
image.
resource.RLIMIT_CPU
The maximum amount of processor time (in seconds) that a process
can use. If this limit is exceeded, a "SIGXCPU" signal is sent to
the process. (See the "signal" module documentation for information
about how to catch this signal 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 only affects 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 for "RLIMIT_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
spend under 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
or used by all of this user id’s processes. This limit is enforced
only if bit 1 of the vm.overcommit sysctl is set. Please see
*tuning(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.
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 either the current process or its children, as
specified by the *who* parameter. The *who* parameter should be
specified using one of the "RUSAGE_*" constants described below.
The fields of the return value each describe how a particular
system resource has been used, e.g. amount of time spent running is
user mode or number of times the process was swapped out of main
memory. Some values are dependent on the clock 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 16 elements.
The fields "ru_utime" and "ru_stime" of the return value are
floating point values representing the amount of time spent
executing in user mode and the amount of time spent executing in
system mode, respectively. The remaining values are integers.
Consult the *getrusage(2)* man page for detailed 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 a "ValueError" if an invalid *who*
parameter is specified. It may also raise "error" exception in
unusual circumstances.
resource.getpagesize()
Returns the number of bytes in a system page. (This need not be the
same as the hardware page size.)
The following "RUSAGE_*" symbols are passed to the "getrusage()"
function to specify which processes information should be provided
for.
resource.RUSAGE_SELF
Pass to "getrusage()" to request resources consumed by the calling
process, which is the sum of resources used by all threads in the
process.
resource.RUSAGE_CHILDREN
Pass to "getrusage()" to request resources consumed by child
processes of the calling process which have been terminated and
waited for.
resource.RUSAGE_BOTH
Pass to "getrusage()" to request resources consumed by both the
current process and child processes. May not be available on all
systems.
resource.RUSAGE_THREAD
Pass to "getrusage()" to request resources consumed by the current
thread. May not be available on all systems.
New in version 3.2.
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