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Linux IPv6 HOWTO (en)
PrevChapter 11. Kernel settings in /proc-filesystemNext

11.1. How to access the /proc-filesystem

11.1.1. Using "cat" and "echo"

Using "cat" and "echo" is the simplest way to access the /proc filesystem, but some requirements are needed for that

  • The /proc-filesystem had to be enabled in kernel, means on compiling following switch has to be set 

CONFIG_PROC_FS=y

  • The /proc-filesystem was mounted before, which can be tested using 

# mount | grep "type proc"
none on /proc type proc (rw)

  • You need read and sometimes also write access (normally root only) to the /proc-filesystem

Normally, only entries in /proc/sys/* are writable, the others are readonly and for information retrieving only.

11.1.1.1. Retrieving a value

The value of an entry can be retrieved using "cat": 

# cat /proc/sys/net/ipv6/conf/all/forwarding
0

11.1.1.2. Setting a value

A new value can be set (if entry is writable) using "echo": 

# echo "1" >/proc/sys/net/ipv6/conf/all/forwarding

11.1.2. Using "sysctl"

Using the "sysctl" program to access the kernel switches is a modern method today. You can use it also, if the /proc-filesystem isn't mounted. But you have only access to /proc/sys/*!

The program "sysctl" is included in package "procps" (on Red Hat Linux systems).

  • The sysctl-interface had to be enabled in kernel, means on compiling following switch has to be set 

CONFIG_SYSCTL=y

11.1.2.1. Retrieving a value

The value of an entry can be retrieved now: 

# sysctl net.ipv6.conf.all.forwarding
net.ipv6.conf.all.forwarding = 0

11.1.2.2. Setting a value

A new value can be set (if entry is writable): 

# sysctl -w net.ipv6.conf.all.forwarding=1
net.ipv6.conf.all.forwarding = 1

Note: Don't use spaces around the "=" on setting values. Also on multiple values per line, quote them like e.g. 

# sysctl -w net.ipv4.ip_local_port_range="32768 61000"
net.ipv4.ip_local_port_range = 32768 61000

11.1.2.3. Additionals

Note: There are sysctl versions in the wild which displaying "/" instead of the "."

For more details take a look into sysctl's manpage.

Hint: for digging fast into the settings, use the option "-a" (display all entries) in conjunction with "grep".

11.1.3. Values found in /proc-filesystems

There are several formats seen in /proc-filesystem:

  • BOOLEAN: simple a "0" (false) or a "1" (true)

  • INTEGER: an integer value, can be unsigned, too

  • more sophisticated lines with several values: sometimes a header line is displayed also, if not, have a look into the kernel source to retrieve information about the meaning of each value...

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