@node Resource Usage And Limitation, Non-Local Exits, Date and Time, Top
@c %MENU% Functions for examining resource usage and getting and setting limits
@chapter Resource Usage And Limitation
This chapter describes functions for examining how much of various kinds of
resources (CPU time, memory, etc.) a process has used and getting and setting
limits on future usage.

@menu
* Resource Usage::		Measuring various resources used.
* Limits on Resources::		Specifying limits on resource usage.
* Priority::			Reading or setting process run priority.
@end menu


@node Resource Usage
@section Resource Usage

@pindex sys/resource.h
The function @code{getrusage} and the data type @code{struct rusage}
are used to examine the resource usage of a process.  They are declared
in @file{sys/resource.h}.

@comment sys/resource.h
@comment BSD
@deftypefun int getrusage (int @var{processes}, struct rusage *@var{rusage})
This function reports resource usage totals for processes specified by
@var{processes}, storing the information in @code{*@var{rusage}}.

In most systems, @var{processes} has only two valid values:

@table @code
@comment sys/resource.h
@comment BSD
@item RUSAGE_SELF
Just the current process.

@comment sys/resource.h
@comment BSD
@item RUSAGE_CHILDREN
All child processes (direct and indirect) that have already terminated.
@end table

In the GNU system, you can also inquire about a particular child process
by specifying its process ID.

The return value of @code{getrusage} is zero for success, and @code{-1}
for failure.

@table @code
@item EINVAL
The argument @var{processes} is not valid.
@end table
@end deftypefun

One way of getting resource usage for a particular child process is with
the function @code{wait4}, which returns totals for a child when it
terminates.  @xref{BSD Wait Functions}.

@comment sys/resource.h
@comment BSD
@deftp {Data Type} {struct rusage}
This data type stores various resource usage statistics.  It has the
following members, and possibly others:

@table @code
@item struct timeval ru_utime
Time spent executing user instructions.

@item struct timeval ru_stime
Time spent in operating system code on behalf of @var{processes}.

@item long int ru_maxrss
The maximum resident set size used, in kilobytes.  That is, the maximum
number of kilobytes of physical memory that @var{processes} used
simultaneously.

@item long int ru_ixrss
An integral value expressed in kilobytes times ticks of execution, which
indicates the amount of memory used by text that was shared with other
processes.

@item long int ru_idrss
An integral value expressed the same way, which is the amount of
unshared memory used for data.

@item long int ru_isrss
An integral value expressed the same way, which is the amount of
unshared memory used for stack space.

@item long int ru_minflt
The number of page faults which were serviced without requiring any I/O.

@item long int ru_majflt
The number of page faults which were serviced by doing I/O.

@item long int ru_nswap
The number of times @var{processes} was swapped entirely out of main memory.

@item long int ru_inblock
The number of times the file system had to read from the disk on behalf
of @var{processes}.

@item long int ru_oublock
The number of times the file system had to write to the disk on behalf
of @var{processes}.

@item long int ru_msgsnd
Number of IPC messages sent.

@item long int ru_msgrcv
Number of IPC messages received.

@item long int ru_nsignals
Number of signals received.

@item long int ru_nvcsw
The number of times @var{processes} voluntarily invoked a context switch
(usually to wait for some service).

@item long int ru_nivcsw
The number of times an involuntary context switch took place (because
a time slice expired, or another process of higher priority was
scheduled).
@end table
@end deftp

@code{vtimes} is a historical function that does some of what
@code{getrusage} does.  @code{getrusage} is a better choice.

@code{vtimes} and its @code{vtimes} data structure are declared in
@file{sys/vtimes.h}.
@pindex sys/vtimes.h
@comment vtimes.h

@deftypefun int vtimes (struct vtimes @var{current}, struct vtimes @var{child})

@code{vtimes} reports resource usage totals for a process.

If @var{current} is non-null, @code{vtimes} stores resource usage totals for
the invoking process alone in the structure to which it points.  If
@var{child} is non-null, @code{vtimes} stores resource usage totals for all
past children (which have terminated) of the invoking process in the structure
to which it points.

@deftp {Data Type} {struct vtimes}
This data type contains information about the resource usage of a process.
Each member corresponds to a member of the @code{struct rusage} data type
described above.

@table @code
@item vm_utime
User CPU time.  Analogous to @code{ru_utime} in @code{struct rusage}
@item vm_stime
System CPU time.  Analogous to @code{ru_stime} in @code{struct rusage}
@item vm_idsrss
Data and stack memory.  The sum of the values that would be reported as
@code{ru_idrss} and @code{ru_isrss} in @code{struct rusage}
@item vm_ixrss
Shared memory.  Analogous to @code{ru_ixrss} in @code{struct rusage}
@item vm_maxrss
Maximent resident set size.  Analogous to @code{ru_maxrss} in
@code{struct rusage}
@item vm_majflt
Major page faults.  Analogous to @code{ru_majflt} in @code{struct rusage}
@item vm_minflt
Minor page faults.  Analogous to @code{ru_minflt} in @code{struct rusage}
@item vm_nswap
Swap count.  Analogous to @code{ru_nswap} in @code{struct rusage}
@item vm_inblk
Disk reads.  Analogous to @code{ru_inblk} in @code{struct rusage}
@item vm_oublk
Disk writes.  Analogous to @code{ru_oublk} in @code{struct rusage}
@end table
@end deftp


The return value is zero if the function succeeds; @code{-1} otherwise.



@end deftypefun
An additional historical function for examining resource usage,
@code{vtimes}, is supported but not documented here.  It is declared in
@file{sys/vtimes.h}.

@node Limits on Resources
@section Limiting Resource Usage
@cindex resource limits
@cindex limits on resource usage
@cindex usage limits

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 resource.  Each
process initially inherits its limit values from its parent, but it can
subsequently change them.

There are two per-process limits associated with a resource:
@cindex limit

@table @dfn
@item current limit
The current limit is the value the system will not allow usage to
exceed.  It is also called the ``soft limit'' because the process being
limited can generally raise the current limit at will.
@cindex current limit
@cindex soft limit

@item maximum limit
The maximum limit is the maximum value to which a process is allowed to
set its current limit.  It is also called the ``hard limit'' because
there is no way for a process to get around it.  A process may lower
its own maximum limit, but only the superuser may increase a maximum
limit.
@cindex maximum limit
@cindex hard limit
@end table

@pindex sys/resource.h
The symbols for use with @code{getrlimit}, @code{setrlimit},
@code{getrlimit64}, and @code{seterlimit64} are defined in
@file{sys/resource.h}.

@comment sys/resource.h
@comment BSD
@deftypefun int getrlimit (int @var{resource}, struct rlimit *@var{rlp})
Read the current and maximum limits for the resource @var{resource}
and store them in @code{*@var{rlp}}.

The return value is @code{0} on success and @code{-1} on failure.  The
only possible @code{errno} error condition is @code{EFAULT}.

When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is in fact @code{getrlimit64}.  Thus, the
LFS interface transparently replaces the old interface.
@end deftypefun

@comment sys/resource.h
@comment Unix98
@deftypefun int getrlimit64 (int @var{resource}, struct rlimit64 *@var{rlp})
This function is similar to @code{getrlimit} but its second parameter is
a pointer to a variable of type @code{struct rlimit64}, which allows it
to read values which wouldn't fit in the member of a @code{struct
rlimit}.

If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit machine, this function is available under the name
@code{getrlimit} and so transparently replaces the old interface.
@end deftypefun

@comment sys/resource.h
@comment BSD
@deftypefun int setrlimit (int @var{resource}, const struct rlimit *@var{rlp})
Store the current and maximum limits for the resource @var{resource}
in @code{*@var{rlp}}.

The return value is @code{0} on success and @code{-1} on failure.  The
following @code{errno} error condition is possible:

@table @code
@item EPERM
@itemize @bullet
@item
The process tried to raise a current limit beyond the maximum limit.

@item
The process tried to raise a maximum limit, but is not superuser.
@end itemize
@end table

When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit system this function is in fact @code{setrlimit64}.  Thus, the
LFS interface transparently replaces the old interface.
@end deftypefun

@comment sys/resource.h
@comment Unix98
@deftypefun int setrlimit64 (int @var{resource}, const struct rlimit64 *@var{rlp})
This function is similar to @code{setrlimit} but its second parameter is
a pointer to a variable of type @code{struct rlimit64} which allows it
to set values which wouldn't fit in the member of a @code{struct
rlimit}.

If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
32-bit machine this function is available under the name
@code{setrlimit} and so transparently replaces the old interface.
@end deftypefun

@comment sys/resource.h
@comment BSD
@deftp {Data Type} {struct rlimit}
This structure is used with @code{getrlimit} to receive limit values,
and with @code{setrlimit} to specify limit values for a particular process
and resource.  It has two fields:

@table @code
@item rlim_t rlim_cur
The current limit

@item rlim_t rlim_max
The maximum limit.
@end table

For @code{getrlimit}, the structure is an output; it receives the current
values.  For @code{setrlimit}, it specifies the new values.
@end deftp

For the LFS functions a similar type is defined in @file{sys/resource.h}.

@comment sys/resource.h
@comment Unix98
@deftp {Data Type} {struct rlimit64}
This structure is analogous to the @code{rlimit} structure above, but
its components have wider ranges.  It has two fields:

@table @code
@item rlim64_t rlim_cur
This is analogous to @code{rlimit.rlim_cur}, but with a different type.

@item rlim64_t rlim_max
This is analogous to @code{rlimit.rlim_max}, but with a different type.
@end table

@end deftp

Here is a list of resources for which you can specify a limit.  Memory
and file sizes are measured in bytes.

@table @code
@comment sys/resource.h
@comment BSD
@item RLIMIT_CPU
@vindex RLIMIT_CPU
The maximum amount of CPU time the process can use.  If it runs for
longer than this, it gets a signal: @code{SIGXCPU}.  The value is
measured in seconds.  @xref{Operation Error Signals}.

@comment sys/resource.h
@comment BSD
@item RLIMIT_FSIZE
@vindex RLIMIT_FSIZE
The maximum size of file the process can create.  Trying to write a
larger file causes a signal: @code{SIGXFSZ}.  @xref{Operation Error
Signals}.

@comment sys/resource.h
@comment BSD
@item RLIMIT_DATA
@vindex 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.

@comment sys/resource.h
@comment BSD
@item RLIMIT_STACK
@vindex RLIMIT_STACK
The maximum stack size for the process.  If the process tries to extend
its stack past this size, it gets a @code{SIGSEGV} signal.
@xref{Program Error Signals}.

@comment sys/resource.h
@comment BSD
@item RLIMIT_CORE
@vindex 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, then no core
file is created.  So setting this limit to zero prevents core files from
ever being created.

@comment sys/resource.h
@comment BSD
@item RLIMIT_RSS
@vindex 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.

@comment sys/resource.h
@comment BSD
@item RLIMIT_MEMLOCK
The maximum amount of memory that can be locked into physical memory (so
it will never be paged out).

@comment sys/resource.h
@comment BSD
@item 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, @code{fork} will fail
with @code{EAGAIN}.  @xref{Creating a Process}.

@comment sys/resource.h
@comment BSD
@item RLIMIT_NOFILE
@vindex RLIMIT_NOFILE
@itemx RLIMIT_OFILE
@vindex RLIMIT_OFILE
The maximum number of files that the process can open.  If it tries to
open more files than this, its open attempt fails with @code{errno}
@code{EMFILE}.  @xref{Error Codes}.  Not all systems support this limit;
GNU does, and 4.4 BSD does.

@comment sys/resource.h
@comment Unix98
@item RLIMIT_AS
@vindex RLIMIT_AS
The maximum size of total memory that this process should get.  If the
process tries to allocate more memory beyond this amount with, for
example, @code{brk}, @code{malloc}, @code{mmap} or @code{sbrk}, the
allocation function fails.

@comment sys/resource.h
@comment BSD
@item RLIM_NLIMITS
@vindex RLIM_NLIMITS
The number of different resource limits.  Any valid @var{resource}
operand must be less than @code{RLIM_NLIMITS}.
@end table

@comment sys/resource.h
@comment BSD
@deftypevr Constant int RLIM_INFINITY
This constant stands for a value of ``infinity'' when supplied as
the limit value in @code{setrlimit}.
@end deftypevr


The following are historical functions to do some of what the functions
above do.  The functions above are better choices.

@code{ulimit} and the command symbols are declared in @file{ulimit.h}.
@pindex ulimit.h
@comment ulimit.h

@deftypefun int ulimit (int @var{cmd}, ...)

@code{ulimit} gets the current limit or sets the current and maximum
limit for a particular resource for the calling process according to the
command @var{cmd}.a

If you are getting a limit, the command argument is the only argument.
If you are setting a limit, there is a second argument:
@code{long int} @var{limit} which is the value to which you are setting
the limit.

The @var{cmd} values and the operations they specify are:
@table @code

@item GETFSIZE
Get the current limit on the size of a file, in units of 512 bytes.

@item SETFSIZE
Set the current and maximum limit on the size of a file to @var{limit} *
512 bytes.

@end table

There are also some other @var{cmd} values that may do things on some
systems, but they are not supported.

Only the superuser may increase a maximum limit.

When you successfully get a limit, the return value of @code{ulimit} is
that limit, which is never negative.  When you successfully set a limit,
the return value is zero.  When the function fails, the return value is
@code{-1} and @code{errno} is set according to the reason:

@table @code
@item EPERM
A process tried to increase a maximum limit, but is not superuser.
@end table


@end deftypefun

@code{vlimit} and its resource symbols are declared in @file{sys/vlimit.h}.
@comment sys/vlimit.h
@pindex sys/vlimit.h
@comment BSD

@deftypefun int vlimit (int @var{resource}, int @var{limit})

@code{vlimit} sets the current limit for a resource for a process.

@var{resource} identifies the resource:

@table @code
@item LIM_CPU
Maximum CPU time.  Same as @code{RLIMIT_CPU} for @code{setrlimit}.
@item LIM_FSIZE
Maximum file size.  Same as @code{RLIMIT_FSIZE} for @code{setrlimit}.
@item LIM_DATA
Maximum data memory.  Same as @code{RLIMIT_DATA} for @code{setrlimit}.
@item LIM_STACK
Maximum stack size.  Same as @code{RLIMIT_STACK} for @code{setrlimit}.
@item LIM_CORE
Maximum core file size.  Same as @code{RLIMIT_COR} for @code{setrlimit}.
@item LIM_MAXRSS
Maximum physical memory.  Same as @code{RLIMIT_RSS} for @code{setrlimit}.
@end table

The return value is zero for success, and @code{-1} with @code{errno} set
accordingly for failure:

@table @code
@item EPERM
The process tried to set its current limit beyond its maximum limit.
@end table

@end deftypefun

@node Priority
@section Process Priority
@cindex process priority
@cindex priority of a process

@pindex sys/resource.h
When several processes try to run, their respective priorities determine
what share of the CPU each process gets.  This section describes how you
can read and set the priority of a process.  All these functions and
macros are declared in @file{sys/resource.h}.

The range of valid priority values depends on the operating system, but
typically it runs from @code{-20} to @code{20}.  A lower priority value
means the process runs more often.  These constants describe the range of
priority values:

@table @code
@comment sys/resource.h
@comment BSD
@item PRIO_MIN
@vindex PRIO_MIN
The smallest valid priority value.

@comment sys/resource.h
@comment BSD
@item PRIO_MAX
@vindex PRIO_MAX
The largest valid priority value.
@end table

@comment sys/resource.h
@comment BSD
@deftypefun int getpriority (int @var{class}, int @var{id})
Read the priority of a class of processes; @var{class} and @var{id}
specify which ones (see below).  If the processes specified do not all
have the same priority, this returns the smallest value that any of them
has.

The return value is the priority value on success, and @code{-1} on
failure.  The following @code{errno} error condition are possible for
this function:

@table @code
@item ESRCH
The combination of @var{class} and @var{id} does not match any existing
process.

@item EINVAL
The value of @var{class} is not valid.
@end table

If the return value is @code{-1}, it could indicate failure, or it
could be the priority value.  The only way to make certain is to set
@code{errno = 0} before calling @code{getpriority}, then use @code{errno
!= 0} afterward as the criterion for failure.
@end deftypefun

@comment sys/resource.h
@comment BSD
@deftypefun int setpriority (int @var{class}, int @var{id}, int @var{priority})
Set the priority of a class of processes to @var{priority}; @var{class}
and @var{id} specify which ones (see below).

The return value is @code{0} on success and @code{-1} on failure.  The
following @code{errno} error condition are defined for this function:

@table @code
@item ESRCH
The combination of @var{class} and @var{id} does not match any existing
process.

@item EINVAL
The value of @var{class} is not valid.

@item EPERM
You tried to set the priority of some other user's process, and you
don't have privileges for that.

@item EACCES
You tried to lower the priority of a process, and you don't have
privileges for that.
@end table
@end deftypefun

The arguments @var{class} and @var{id} together specify a set of
processes in which you are interested.  These are the possible values of
@var{class}:

@table @code
@comment sys/resource.h
@comment BSD
@item PRIO_PROCESS
@vindex PRIO_PROCESS
Read or set the priority of one process.  The argument @var{id} is a
process ID.

@comment sys/resource.h
@comment BSD
@item PRIO_PGRP
@vindex PRIO_PGRP
Read or set the priority of one process group.  The argument @var{id} is
a process group ID.

@comment sys/resource.h
@comment BSD
@item PRIO_USER
@vindex PRIO_USER
Read or set the priority of one user's processes.  The argument @var{id}
is a user ID.
@end table

If the argument @var{id} is 0, it stands for the current process,
current process group, or the current user, according to @var{class}.

@c ??? I don't know where we should say this comes from.
@comment Unix
@comment dunno.h
@deftypefun int nice (int @var{increment})
Increment the priority of the current process by @var{increment}.
The return value is the same as for @code{setpriority}.

Here is an equivalent definition of @code{nice}:

@smallexample
int
nice (int increment)
@{
  int old = getpriority (PRIO_PROCESS, 0);
  return setpriority (PRIO_PROCESS, 0, old + increment);
@}
@end smallexample
@end deftypefun