Purpose
Sets
and gets user limits.
Library
Standard
C Library (libc.a)
Syntax
The
syntax for the ulimit subroutine when the Command parameter
specifies a value of GET_FSIZE or SET_FSIZE is:
#include <ulimit.h>
long int ulimit ( Command, NewLimit)
int Command;
off_t NewLimit;
The syntax for the ulimit subroutine when
the Command parameter specifies a value of GET_DATALIM, SET_DATALIM, GET_STACKLIM, SET_STACKLIM, GET_REALDIR,
or SET_REALDIR is:
#include <ulimit.h>
long int ulimit (Command, NewLimit)
int Command;
unsigned long NewLimit;
Description
The ulimit subroutine
controls process limits.
Even with remote
files, the ulimit subroutine values of the process on the client
node are used.
Note: Raising the data ulimit does not necessarily
raise the program break value. If the proper memory segments are not
initialized at program load time, raising your memory limit will not
allow access to this memory. Also, without these memory segments initialized,
the value returned after such a change may not be the proper break
value. If your data limit is RLIM_INFINITY, this value will never
advance past the segment size, even if that data is available. Use
the
-bmaxdata flag of the
ld command to
set up these segments at load time.
Setting an fsize of
2G or more for a 32-bit application will be treated as unlimited.
Parameters
Item |
Description |
Command |
Specifies the form of control. The following Command parameter
values require that the NewLimit parameter be declared as an off_t structure:
- GET_FSIZE (1)
- Returns the process file size limit. The limit is in units of UBSIZE blocks
(see the sys/param.h file) and is inherited by child processes.
Files of any size can be read. The process file size limit is returned
in the off_t structure specified by the NewLimit parameter.
- SET_FSIZE (2)
- Sets the process file size limit to the value in the off_t structure
specified by the NewLimit parameter. Any process can decrease
this limit, but only a process with root user authority can increase
the limit. The new file size limit is returned.
The following Command parameter
values require that the NewLimit parameter be declared as an
integer:
- GET_DATALIM (3)
- Returns the maximum possible break value (as described in the brk or sbrk subroutine).
- SET_DATALIM (1004)
- Sets the maximum possible break value (described in the brk and sbrk subroutines).
Returns the new maximum break value, which is the NewLimit parameter
rounded up to the nearest page boundary.
Note: When a program is executing
using the large address-space model, the operating system attempts
to modify the soft limit on data size, if necessary, to increase it
to match the maxdata value. If the maxdata value is
larger than the current hard limit on data size, either the program
will not execute if the XPG_SUS_ENV environment
variable has the value set to ON, or the soft limit will be set to
the current hard limit. If the maxdata value is smaller than
the size of the program's static data, the program will not execute.
- GET_STACKLIM (1005)
- Returns the lowest valid stack address.
Note: Stacks grow from
high addresses to low addresses.
- SET_STACKLIM (1006)
- Sets the lowest valid stack address. Returns the new minimum
valid stack address, which is the NewLimit parameter rounded
down to the nearest page boundary.
- GET_REALDIR (1007)
- Returns the current value of the real directory read flag.
If this flag is a value of 0, a read system call (or readx with Extension parameter
value of 0) against a directory returns fixed-format entries compatible
with the System V UNIX operating
system. Otherwise, a read system call(or readx with Extension parameter
value of 0) against a directory returns the underlying physical format.
- SET_REALDIR (1008)
- Sets the value of the real directory read flag. If the NewLimit parameter
is a value of 0, this flag is cleared; otherwise, it is set. The old
value of the real directory read flag is returned.
|
NewLimit |
Specifies the new limit. The value and data type or structure
of the NewLimit parameter depends on the Command parameter
value that is used. |
Examples
To
increase the size of the stack by 4096 bytes (use 4096 or PAGESIZE),
and set the rc to the new lowest valid stack address, enter:
rc = ulimit(SET_STACKLIM, ulimit(GET_STACKLIM, 0) - 4096);
Return Values
Upon successful completion, the value of the
requested limit is returned. Otherwise, a value of -1 is returned
and the errno global variable is set to indicate the error.
All return values are permissible if the ulimit subroutine
is successful. To check for error situations, an application should
set the errno global variable to 0 before calling the ulimit subroutine.
If the ulimit subroutine returns a value of -1, the application
should check the errno global variable to verify that it is
nonzero.
Error Codes
The ulimit subroutine
is unsuccessful and the limit remains unchanged if one of the following
is true:
Item |
Description |
EPERM |
A process without root user authority attempts to increase
the file size limit. |
EINVAL |
The Command parameter is a value other than GET_FSIZE, SET_FSIZE, GET_DATALIM, SET_DATALIM, GET_STACKLIM, SET_STACKLIM, GET_REALDIR,
or SET_REALDIR. |