The GNU C Library - Limits on Resources
Node: Limits on Resources
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Limiting Resource Usage
You can specify limits for the resource usage of a process. When the process tries to exceed a limit, it may get a signal, or the system call by which it tried to do so may fail, depending on the limit. Each process initially inherits its limit values from its parent, but it can subsequently change them.
The symbols in this section are defined in `sys/resource.h'.
- Function int getrlimit (int resource, struct rlimit *rlp)
-
Read the current value and the maximum value of resource resource and store them in
*rlp
.
The return value is 0
on success and -1
on failure. The only possible errno
error condition is EFAULT
.
- Function int setrlimit (int resource, struct rlimit *rlp)
-
Store the current value and the maximum value of resource resource in
*rlp
.
The return value is 0
on success and -1
on failure. The following errno
error condition is possible:
-
EPERM
-
You tried to change the maximum permissible limit value, but you don't have privileges to do so.
- Data Type struct rlimit
-
This structure is used with
getrlimit
to receive limit values, and with setrlimit
to specify limit values. It has two fields:
-
rlim_cur
-
The current value of the limit in question. This is also called the ``soft limit''.
-
rlim_max
-
The maximum permissible value of the limit in question. You cannot set the current value of the limit to a larger number than this maximum. Only the super user can change the maximum permissible value. This is also called the ``hard limit''.
In getrlimit
, the structure is an output; it receives the current values. In setrlimit
, it specifies the new values.
Here is a list of resources that you can specify a limit for. Those that are sizes are measured in bytes.
-
RLIMIT_CPU
-
The maximum amount of cpu time the process can use. If it runs for longer than this, it gets a signal:
SIGXCPU
. The value is measured in seconds. See Operation Error Signals.
-
RLIMIT_FSIZE
-
The maximum size of file the process can create. Trying to write a larger file causes a signal:
SIGXFSZ
. See Operation Error Signals.
-
RLIMIT_DATA
-
The maximum size of data memory for the process. If the process tries to allocate data memory beyond this amount, the allocation function fails.
-
RLIMIT_STACK
-
The maximum stack size for the process. If the process tries to extend its stack past this size, it gets a
SIGSEGV
signal. See Program Error Signals.
-
RLIMIT_CORE
-
The maximum size core file that this process can create. If the process terminates and would dump a core file larger than this maximum size, then no core file is created. So setting this limit to zero prevents core files from ever being created.
-
RLIMIT_RSS
-
The maximum amount of physical memory that this process should get. This parameter is a guide for the system's scheduler and memory allocator; the system may give the process more memory when there is a surplus.
-
RLIMIT_MEMLOCK
-
The maximum amount of memory that can be locked into physical memory (so it will never be paged out).
-
RLIMIT_NPROC
-
The maximum number of processes that can be created with the same user ID. If you have reached the limit for your user ID,
fork
will fail with EAGAIN
. See Creating a Process.
-
RLIMIT_NOFILE
-
-
RLIMIT_OFILE
-
The maximum number of files that the process can open. If it tries to open more files than this, it gets error code
EMFILE
. See Error Codes. Not all systems support this limit; GNU does, and 4.4 BSD does.
-
RLIM_NLIMITS
-
The number of different resource limits. Any valid resource operand must be less than
RLIM_NLIMITS
.
- Constant int RLIM_INFINITY
-
This constant stands for a value of ``infinity'' when supplied as the limit value in
setrlimit
.
Two historical functions for setting resource limits, ulimit
and vlimit
, are not documented here. The latter is declared in `sys/vlimit.h' and comes from BSD.
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