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Commands Reference, Volume 5
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ulimit Command
Purpose
Sets or reports user resource limits.
Syntax
ulimit [ -H ] [ -S ] [ -a ] [ -c ] [ -d ] [ -f ] [ -m ] [ -n ] [ -s ] [ -t ] [
Limit ]
Description
The ulimit command sets or reports user process resource limits, as defined in
the /etc/security/limits file. This file contains these default limits:
fsize = 2097151
core = 2097151
cpu = -1
data = 262144
rss = 65536
stack = 65536
nofiles = 2000
These values are used as default settings when a new user is added to the
system. The values are set with the mkuser command when the user is added to the
system, or changed with the chuser command.
Limits are categorized as either soft or hard. With the ulimit command, you can
change your soft limits, up to the maximum set by the hard limits. You must have
root user authority to change resource hard limits.
Many systems do not contain one or more of these limits. The limit for a
specified resource is set when the Limit parameter is specified. The value of
the Limit parameter can be a number in the unit specified with each resource, or
the value unlimited. To set the specific ulimit to unlimited, use the word
unlimited
Note: Setting the default limits in the /etc/security/limits file sets
system wide limits, not just limits taken on by a user when that user is
created.
The current resource limit is printed when you omit the Limit parameter. The
soft limit is printed unless you specify the -H flag. When you specify more than
one resource, the limit name and unit is printed before the value. If no option
is given, the -f flag is assumed.
Since the ulimit command affects the current shell environment, it is provided
as a shell regular built-in command. If this command is called in a separate
command execution environment, it does not affect the file size limit of the
caller's environment. This would be the case in the following examples:
nohup ulimit -f 10000
env ulimit 10000
Once a hard limit has been decreased by a process, it cannot be increased
without root privilege, even to revert to the original limit.
For more information about user and system resource limits, refer to the
getrlimit, setrlimit, or vlimit subroutine in AIX Version 4.3 Technical
Reference: Base Operating System and Extensions Volume 1.
Flags
-a Lists all of the current resource limits.
-c Specifies the size of core dumps, in number of 512-byte blocks.
-d Specifies the size of the data area, in number of K bytes.
-f Sets the file size limit in blocks when the Limit parameter is used, or
reports the file size limit if no parameter is specified. The -f flag is the
default.
-H Specifies that the hard limit for the given resource is set. If you have root
user authority, you can increase the hard limit. Anyone can decrease it.
-m Specifies the size of physical memory, in number of K bytes.
-n Specifies the limit on the number of file descriptors a process may have.
-s Specifies the stack size, in number of K bytes.
-S Specifies that the soft limit for the given resource is set. A soft limit can
be increased up to the value of the hard limit. If neither the -H nor -S flags
are specified, the limit applies to both.
-t Specifies the number of seconds to be used by each process.
Exit Status
The following exit values are returned:
0 Successful completion.
>0 A request for a higher limit was rejected or an error occurred.
Example
To set the file size limit to 51,200 bytes, enter:
ulimit -f 100
Files
/usr/bin/ksh Contains the ulimit built-in command.
Related Information
The ksh command.
The ulimit subroutine, getrlimit, setrlimit, or vlimit subroutine in AIX Version
4.3 Technical Reference: Base Operating System and Extensions Volume 1.
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