libc/sys/getrlimit.2

.\"	$NetBSD: getrlimit.2,v 1.21 2002/02/08 01:28:18 ross Exp $
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.\"     @(#)getrlimit.2	8.1 (Berkeley) 6/4/93
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.Dd November 23, 2001
.Dt GETRLIMIT 2
.Os
.Sh NAME
.Nm getrlimit ,
.Nm setrlimit
.Nd control maximum system resource consumption
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.Fd #include \*[Lt]sys/resource.h\*[Gt]
.Ft int
.Fn getrlimit "int resource" "struct rlimit *rlp"
.Ft int
.Fn setrlimit "int resource" "const struct rlimit *rlp"
.Sh DESCRIPTION
Limits on the consumption of system resources by the current process
and each process it creates may be obtained with the
.Fn getrlimit
call, and set with the
.Fn setrlimit
call.  Resources of an arbitrary process can be obtained/changed using
.Xr sysctl 3 .
..
.Pp
The
.Fa resource
parameter is one of the following:
.Bl -tag -width RLIMIT_FSIZEAA
.It Li RLIMIT_CORE
The largest size (in bytes)
.Pa core
file that may be created.
.It Li RLIMIT_CPU
The maximum amount of cpu time (in seconds) to be used by
each process.
.It Li RLIMIT_DATA
The maximum size (in bytes) of the data segment for a process;
this defines how far a program may extend its break with the
.Xr sbrk 2
system call.
.It Li RLIMIT_FSIZE
The largest size (in bytes) file that may be created.
.It Li RLIMIT_MEMLOCK
The maximum size (in bytes) which a process may lock into memory
using the
.Xr mlock 2
function.
.It Li RLIMIT_NOFILE
The maximum number of open files for this process.
.It Li RLIMIT_NPROC
The maximum number of simultaneous processes for this user id.
.It Li RLIMIT_RSS
The maximum size (in bytes) to which a process's resident set size may
grow.
This imposes a limit on the amount of physical memory to be given to
a process; if memory is tight, the system will prefer to take memory
from processes that are exceeding their declared resident set size.
.It Li RLIMIT_STACK
The maximum size (in bytes) of the stack segment for a process;
this defines how far a program's stack segment may be extended.
Stack extension is performed automatically by the system.
.El
.Pp
A resource limit is specified as a soft limit and a hard limit.  When a
soft limit is exceeded a process may receive a signal (for example, if
the cpu time or file size is exceeded), but it will be allowed to
continue execution until it reaches the hard limit (or modifies
its resource limit).  The
.Em rlimit
structure is used to specify the hard and soft limits on a resource,
.Bd -literal -offset indent
struct rlimit {
	rlim_t	rlim_cur;	/* current (soft) limit */
	rlim_t	rlim_max;	/* hard limit */
};
.Ed
.Pp
Only the super-user may raise the maximum limits.  Other users
may only alter
.Fa rlim_cur
within the range from 0 to
.Fa rlim_max
or (irreversibly) lower
.Fa rlim_max .
.Pp
An
.Dq infinite
value for a limit is defined as
.Dv RLIM_INFINITY .
.Pp
Because this information is stored in the per-process information,
this system call must be executed directly by the shell if it
is to affect all future processes created by the shell.
Thus, shells provide built-in commands to change the limits
.Ic ( limit
for
.Xr csh 1 ,
or
.Ic ulimit
for
.Xr sh 1 ) .
.Pp
The system refuses to extend the data or stack space when the limits
would be exceeded in the normal way: a
.Xr brk 2
call fails if the data space limit is reached.
When the stack limit is reached, the process receives
a segmentation fault
.Pq Dv SIGSEGV ;
if this signal is not
caught by a handler using the signal stack, this signal
will kill the process.
.Pp
A file I/O operation that would create a file larger that the process'
soft limit will cause the write to fail and a signal
.Dv SIGXFSZ
to be
generated; this normally terminates the process, but may be caught.  When
the soft cpu time limit is exceeded, a signal
.Dv SIGXCPU
is sent to the
offending process.
.Sh RETURN VALUES
A 0 return value indicates that the call succeeded, changing
or returning the resource limit.  Otherwise, -1 is returned
and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn getrlimit
and
.Fn setrlimit
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The address specified for
.Fa rlp
is invalid.
.It Bq Er EINVAL
Specified
.Fa resource
was invalid.
.It Bq Er EINVAL
In the
.Fn setrlimit
call, the specified
.Fa rlim_cur
exceeds the specified
.Fa rlim_max .
.It Bq Er EPERM
The limit specified to
.Fn setrlimit
would have
raised the maximum limit value, and the caller is not the super-user.
.El
.Pp
The
.Fn setrlimit
function may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The limit specified to
.Fn setrlimit
cannot be lowered, because current usage is already higher than the limit.
.El
.Sh SEE ALSO
.Xr csh 1 ,
.Xr sh 1 ,
.Xr quotactl 2 ,
.Xr sigaction 2 ,
.Xr sigaltstack 2 ,
.Xr sysctl 3
.\" Sh STANDARDS
.\" With exception of
.\" .Li RLIMIT_AS
.\" (which is not currently supported), the
.\" .Fn getrlimit
.\" and
.\" .Fn setrlimit
.\" functions conform to
.\" .St -susv2 .
.Sh HISTORY
The
.Fn getrlimit
function call appeared in
.Bx 4.2 .