Why can not change the file /proc/sys/net/ipv4/ip_forward?

Question

$ sudo echo 1 >/proc/sys/net/ipv4/ip_forward 
bash: /proc/sys/net/ipv4/ip_forward: Permission denied

then I try to get write privilege, also failed.

$ sudo chmod a+wx /proc/sys/net/ipv4/ip_forward 
chmod: changing permissions of `/proc/sys/net/ipv4/ip_forward': Operation not permitted

what is wrong?

Answer 1

You are trying to change the kernel values. Be sure of what you are doing.

Okay here is how you can change the value of ip_forward with root privilege (sudo -i)

• First check the value of ip_forward using command: sysctl -a | grep ip_forward
• Now using sysctl -w <parameter=value> you change the value of ip_forward:
  • sysctl -w ip_forward=1
• Make these changes to reflect in kernel using: sysctl -p
• Do the first step once again to check the values.

I recommend you to go through the man page of sysctl

Answer 2

Edit file /etc/sysctl.conf and edit this section:

#net.ipv4.ip_forward = 0

to

net.ipv4.ip_forward = 1 (remove # sign)

then type command: sysctl -p
Last, reboot your system.

Answer 3

To change this kernel value in kernel version 4.4+ (Ubuntu 16.04+), you need to do the following:

sudo sysctl -w net.ipv4.ip_forward=1

Answer 4

Terminal:

sudo nano /proc/sys/net/ipv4 ip_forward

after change it, save with CTRL + O and exit with CTRL + X