Red Hat LINUX 7.2 Reference Manual page 93

Section 4.3:Directories in /proc
• rtsig-nr — The current number of POSIX realtime signals queued by the kernel.
• sem — This file configures semaphore settings within the kernel. A semaphore is a System V
IPC object that is used to control utilization of a particular process.
• shmall — Sets the total amount of shared memory that can be used at one time on the system,
in bytes. By default, this value is 2097152.
• shmmax — Sets the largest shared memory segment size allowed by the kernel, in bytes. By
default, this value is 33554432. The kernel supports much larger values than this, however.
• shmmni — Sets the maximum number of shared memory segments for the whole system. By
default, this value is 4096
• sysrq — Activates the System Request Key, if this value is set to anything other than the default
of 0.
• threads-max — Sets the maximum number of threads to be used by the kernel, with a default
value of 4095.
• version — Displays the date and time the kernel was last compiled. The first field in this file,
such as #3, relates to the number of times a kernel was built from the source base.
The random directory stores a number of values related to generating random numbers for the kernel.
/proc/sys/net
This directory contains assorted directories of its own concerning various networking topics, including
assorted protocols and centers of emphasis. Various configurations at the time of kernel compilation
make available different directories here, such as appletalk, ethernet, ipv4, ipx, and ipv6.
Within these directories, you can adjust the assorted networking values for that configuration on a
running system.
Given the wide variety of possible networking options available with Linux and the great amount of
space required to discuss them, only the most common /proc/sys/net directories will be dis-
cussed.
The core directory contains a variety of settings that control the interaction between the kernel and
networking layers. The most important files there are:
• message_burst — Tenths of seconds required to write a new warning message. This is used
to prevent Denial of Service (DoS) attacks, and the default setting is 50.
• message_cost — Also used to prevent DoS attacks by placing a cost on every warning mes-
sage. The higher the value of this file (default of 5), the more likely the warning message will be
ignored.
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