On Thu, Dec 24, 2020 at 12:49:30PM +0800, zhang yang wrote: > IP_ dynaddr > To modify and save the prompt: "IP"_ dynaddr" E212: Can't open file for > writing“. > So I used Chmod 777 ip_ dynaddr authority, display error: Chmod: changing > permissions of 'IP_ dynaddr': Operation not permitted. > I use chaddr - i ip_dynaddr command to removes attributes and displays an > error: chattr: Inappropriate ioctl for device while reading flags on > ip_dynaddr. How to set dynaddr?
For the benefit of others, the file in question is /proc/sys/net/ipv4/ip_dynaddr /proc is not a regular file system. It's an interface to pieces of the kernel. Some of these pieces can be read by everyone. Almost none of them can be *written* by everyone -- you usually have to be root to write to them. chmod 777 is almost always a *huge* mistake. If the permissions on a file are stopping you from doing someting, there's usually a reason for that. Destroying the permissions on the file is not the right answer. Elevating yourself to a higher power level is. Now, the next thing you'll want to know is that while root can probably write to this file, it can't necessary *edit* the file with a text editor. You're expected to use a much lower level of access to open the file, write to it, and close it. Typically that's done with echo something > /proc/whatever Of course this redirection means that it's your shell who needs privileges to open the file for writing. If you try it as your regular user, you'll encounter the "permission denied" error that you already saw. The expected course of action is for you to do it from a root shell, which you obtain by using su or sudo. $ su Password: # echo something > /proc/whatever # exit $ If you're not a fan of su, or if you're one of those people who has decided not to have a root password (a bad idea!), then you can get a root shell with sudo -s: $ sudo -s # echo something >/proc/whatever # exit $ (sudo may prompt you for your password if you haven't used sudo in that terminal in the last few minutes.) Some people will try to be clever and do this: sudo echo something > /proc/whatever That will not work, for the reasons explained at <https://mywiki.wooledge.org/BashPitfalls#pf53>. You may use one of the quoted forms on that page if you prefer. But the original design of the files in /proc was for users with a root shell to perform shell redirections. Not for sudo. Also, while I'm here talking about su, bear in mind that Debian decided to become more like Red Hat and replaced their version of su with the one used by Red Hat, and didn't bother configuring it to maintain backward compatibility with the previous version. See <https://wiki.debian.org/NewInBuster#Changes> for workarounds, including how to configure su to behave sanely.
