Chapter 2. The

proc

File System

47

  dentry state

  Provides the status of the directory cache. The file looks similar to this:

57411 52939 45 0 0 0

The first number reveals the total number of directory cache entries, while the second number

displays the number of unused entries. The third number tells the number of seconds between when

a directory has been freed and when it can be reclaimed, and the fourth measures the pages currently

requested by the system. The last two numbers are not used and currently display only zeros.

  dquot nr

  Shows the maximum number of cached disk quota entries.

  file max

  Allows you to change the maximum number of file handles that the kernel will

allocate. Raising the value in this file can resolve errors caused by a lack of available file handles.

  file nr

  Displays the number of allocated file handles, used file handles, and the maximum

number of file handles.

  overflowgid

and

overflowuid

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

with file systems that only support 16 bit group and user IDs.

  super max

  Controls the maximum number of superblocks available.

  super nr

  Displays the current number of superblocks in use.

2.3.9.3.

/proc/sys/kernel/

This directory contains a variety of different configuration files that directly affect the operation of the

kernel. Some of the most important files include:

  acct

  Controls the suspension of process accounting based on the percentage of free space

available on the file system containing the log. By default, the file looks like this:

4 2 30

The second value sets the threshold percentage of free space when logging will be suspended, while

the first value dictates the percentage of free space required for logging to resume. The third value

sets the interval in seconds that the kernel polls the file system to see if logging should be suspended

or resumed.

  cap bound

  Controls the capability bounding settings, which provide a list of capabilities for any

process on the system. If a capability is not listed here, then no process, no matter how privileged,

can do it. The idea is to make the system more secure by ensuring that certain things cannot happen,

at least beyond a certain point in the boot process.

The various values that are possible here are beyond the scope of this manual, so consult the kernel

documentation for more information.

  ctrl alt del

  Controls whether [Ctrl] [Alt] [Delete] will gracefully restart the computer us 

ing

init

(value

0

) or force an immediate reboot without syncing the dirty buffers to disk (value

1

).

  domainname

  Allows you to configure the system's domain name, such as

subgenius.com

.

  hostname

  Allows you to configure the system's host name, such as

bob.subgenius.com

.

  hotplug

  Configures the utility to be used when a configuration change is detected by the system.

This is primarily used with USB and Cardbus PCI. The default value of

/sbin/hotplug

should

not be changed unless you are testing a new program to fulfill this role.

  modprobe

  Sets the location of the program to be used to load kernel modules when necessary.

The default value of

/sbin/modprobe

signifies that

kmod

will call it to actually load the module

when a kernel thread calls

kmod

.

  msgmax

  Sets the maximum size of any message sent from one process to another is set to

8192

bytes by default. You should be careful about raising this value, as queued messages between