overcommit_memory — Configures the conditions under which a large memory request is accepted or denied. The following three modes are available:
0 — The kernel performs heuristic memory overcommit handling, by estimating the amount of memory available and failing requests that are blatantly invalid. Unfortunately, since memory is allocated using a heuristic rather than a precise algorithm, this setting can sometimes allow overloading the memory available on a system. This is the default setting.
1 — The kernel performs no memory overcommit handling. Under this setting, the potential for memory overload is increased, but so is performance for memory intensive tasks (such as those executed by some scientific software).
2 — The kernel fails requests for memory that add up to all of swap plus the percent of physical RAM specified in /proc/sys/vm/overcommit_ratio. This setting is best for those who desire less risk of memory overcommitment.
Note This setting is only recommended for systems with swap areas larger than physical memory.
overcommit_ratio — Specifies the percentage of physical RAM considered when /proc/sys/vm/overcommit_memory is set to 2. The default value is 50.
pagecache — Controls the percentage of total system memory used for page cache. The following is a typical output for this file:
1 15 100 |
The first value sets the minimum memory to be used as buffer and page cache memory. The middle value sets the percentage of system memory dedicated to buffer and page cache memory where the memory management subsystem begins to clear buffer cache more than other kinds of memory to compensate for a general lack of free memory. The final value specifies the maximum memory to be used as buffer memory, but is not yet implemented.
page-cluster — Sets the number of pages read in a single attempt. The default value of 3, which actually relates to 16 pages, is appropriate for most systems.
pagetable_cache — Controls the number of page tables that are cached on a per-processor basis. The first and second values relate to the minimum and maximum number of page tables to set aside, respectively.
The /usr/src/linux-2.4/Documentation/sysctl/vm.txt file contains additional information on these files.
5.3.10. /proc/sysvipc/
This directory contains information about System V IPC resources. The files in this directory relate to System V IPC calls for messages (msg), semaphores (sem), and shared memory (shm).
5.3.11. /proc/tty/
This directory contains information about the available and currently used tty devices on the system. Originally called teletype devices, any character-based data terminals are called tty devices.
In Linux, there are three different kinds of tty
devices. Serial devices are used with serial
connections, such as over a modem or using a serial
cable. Virtual terminals create the common
console connection, such as the virtual consoles available when
pressing
serial /dev/cua 5 64-127 serial:callout serial /dev/ttyS 4 64-127 serial pty_slave /dev/pts 136 0-255 pty:slave pty_master /dev/ptm 128 0-255 pty:master pty_slave /dev/ttyp 3 0-255 pty:slave pty_master /dev/pty 2 0-255 pty:master /dev/vc/0 /dev/vc/0 4 0 system:vtmaster /dev/ptmx /dev/ptmx 5 2 system /dev/console /dev/console 5 1 system:console /dev/tty /dev/tty 5 0 system:/dev/tty unknown /dev/vc/%d 4 1-63 console |
The /proc/tty/driver/serial file lists the usage statistics and status of each of the serial tty lines.
In order for tty devices to be used as network devices, the Linux kernel enforces line discipline on the device. This allows the driver to place a specific type of header with every block of data transmitted over the device, making it possible for the remote end of the connection to a block of data as just one in a stream of data blocks. SLIP and PPP are common line disciplines, and each are commonly used to connect systems to one other over a serial link.
Registered line disciplines are stored in the ldiscs file, and more detailed information is available within the ldisc/ directory.