Installation guide

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