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.

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

# 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
   

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

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

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

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...