48

Chapter 2. The

proc

File System

processes are stored in non swappable kernel memory. Any increase in

msgmax

would increase

RAM requirements for the system.

  msgmnb

  Sets the maximum number of bytes in a single message queue. The default is

16384

.

  msgmni

  Sets the maximum number of message queue identifiers. The default is

16

.

  osrelease

  Lists the Linux kernel release number. This file can only be altered by changing the

kernel source and recompiling.

  ostype

  Displays the type of operating system. By default, this file is set to

Linux

, and this

value can only be changed by changing the kernel source and recompiling.

  overflowgid

and

overflowuid

  Defines the fixed group ID and user ID, respectively, for use

with system calls on architectures that only support 16 bit group and user IDs.

  panic

  Defines the number of seconds the kernel will postpone rebooting when the system

experiences a kernel panic. By default, the value is set to

0

, which disables automatic rebooting

after a panic.

  printk

  This file controls a variety of settings related to printing or logging error messages. Each

error message reported by the kernel has a loglevel associated with it that defines the importance of

the message. The loglevel values break down in this order:

0

  Kernel emergency. The system is unusable.

1

  Kernel alert. Action must be taken immediately.

2

  Condition of the kernel is considered critical.

3

  General kernel error condition.

4

  General kernel warning condition.

5

  Kernel notice of a normal but significant condition.

6

  Kernel informational message.

7

  Kernel debug level messages.

Four values are found in the

printk

file:

6 4 1 7

Each of these values defines a different rule for dealing with error messages. The first value, called

the console loglevel, defines the lowest priority of messages that will be printed to the console.

(Note that, the lower the priority, the higher the loglevel number.) The second value sets the default

loglevel for messages without an explicit loglevel attached to them. The third value sets the lowest

possible loglevel configuration for the console loglevel. The last value sets the default value for the

console loglevel.

  rtsig max

  Configures the maximum number of POSIX realtime signals that the system may

have queued at any one time. The default value is

1024

.

  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

. However, the kernel supports much larger values than this.

  shmmni

  Sets the maximum number of shared memory segments for the whole system. By de 

fault, this value is

4096

  sysrq

  Activates the System Request Key, if this value is set to anything other than the default

of

0

. See Section 2.3.9 for details about the System Request Key.