Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Scaricare il pdf (Pagina 51)

Chapter 2. The /proc File System 51

• max_map_count — Conﬁgures the maximum number of memory map areas a process may have.

In most cases, the default value of 65536 is appropriate.

• overcommit_memory — Contains a value that, when set to something other than the default of 0,

allows the kernel to skip a standard check to see if there is enough memory before allocating it.

• pagecache — Controls the amount of memory used by the page cache. The values in page-

cache are percentages, and they work in a similar way as buffermem to enforce minimums and

maximums of available page cache memory.

• page-cluster — Sets the number of pages read in a single attempt. The default value of 4, 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.

Additional information on these various ﬁles can be found in

/usr/src/linux-2.4/Documentation/sysctl/vm.txt.

2.3.9. /proc/sysvipc/

This directory contain 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).

2.3.10. /proc/tty/

This directory contains information about the available and currently used tty devices on the system.

Originally called a teletype device, 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 [Alt]-[

F-key ] at the system console. Pseudo

terminals create a two-way communication that is used by some higher level applications, such as

X11.

The drivers ﬁle is a list of the current tty devices in use:

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 that tty devices can be used in a similar way as network devices, the Linux kernel will enforce

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 be

able to see that 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.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 51

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