01-11-2010
For the third time, I'm sure you have. I'm sure they must be working on correcting the problem that prevents two-gig reads, as well; the sticky issue is likely how to manage that on 32-bit systems.
You weren't the OP, though, and my question was what these enormous reads were for in the first place. 9 out of 10 times I see someone sucking an enormous wad of raw data into RAM, they're not doing it for performance reasons -- they just want it all in RAM to get at it without further system calls. An mmap gets them that without decimating the cache and squeezing frequently-used things into swap for no good reason, and avoids this problem entirely.
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LEARN ABOUT LINUX
pam_limits
PAM_LIMITS(8) Linux-PAM Manual PAM_LIMITS(8)
NAME
pam_limits - PAM module to limit resources
SYNOPSIS
pam_limits.so [change_uid] [conf=/path/to/limits.conf] [debug] [utmp_early] [noaudit]
DESCRIPTION
The pam_limits PAM module sets limits on the system resources that can be obtained in a user-session. Users of uid=0 are affected by this
limits, too.
By default limits are taken from the /etc/security/limits.conf config file. Then individual *.conf files from the /etc/security/limits.d/
directory are read. The files are parsed one after another in the order of "C" locale. The effect of the individual files is the same as if
all the files were concatenated together in the order of parsing. If a config file is explicitly specified with a module option then the
files in the above directory are not parsed.
The module must not be called by a multithreaded application.
If Linux PAM is compiled with audit support the module will report when it denies access based on limit of maximum number of concurrent
login sessions.
OPTIONS
change_uid
Change real uid to the user for who the limits are set up. Use this option if you have problems like login not forking a shell for user
who has no processes. Be warned that something else may break when you do this.
conf=/path/to/limits.conf
Indicate an alternative limits.conf style configuration file to override the default.
debug
Print debug information.
utmp_early
Some broken applications actually allocate a utmp entry for the user before the user is admitted to the system. If some of the services
you are configuring PAM for do this, you can selectively use this module argument to compensate for this behavior and at the same time
maintain system-wide consistency with a single limits.conf file.
noaudit
Do not report exceeded maximum logins count to the audit subsystem.
MODULE TYPES PROVIDED
Only the session module type is provided.
RETURN VALUES
PAM_ABORT
Cannot get current limits.
PAM_IGNORE
No limits found for this user.
PAM_PERM_DENIED
New limits could not be set.
PAM_SERVICE_ERR
Cannot read config file.
PAM_SESSION_ERR
Error recovering account name.
PAM_SUCCESS
Limits were changed.
PAM_USER_UNKNOWN
The user is not known to the system.
FILES
/etc/security/limits.conf
Default configuration file
EXAMPLES
For the services you need resources limits (login for example) put a the following line in /etc/pam.d/login as the last line for that
service (usually after the pam_unix session line):
#%PAM-1.0
#
# Resource limits imposed on login sessions via pam_limits
#
session required pam_limits.so
Replace "login" for each service you are using this module.
SEE ALSO
limits.conf(5), pam.d(5), pam(7).
AUTHORS
pam_limits was initially written by Cristian Gafton <gafton@redhat.com>
Linux-PAM Manual 06/04/2011 PAM_LIMITS(8)