Alter a running process without killing it

[smolloy]

In the comments section of this blog, the commenter "Pratik" claims that you can edit a running bash script, without killing it, and have the changes picked up by the running script. He claims you can do this by editing files in /proc.

Now, I know how to find the /proc folder that contains the data on the running process,

cd /proc/`pgrep process_name`

But I can't figure out what I should do if I want to edit a running bash script.

Can anyone help me with this?

[smolloy]

I guess this is a bit high-level for most folks (including me)

Ah well. Thanks for reading

[Rubberman]

You can do most anything with Linux, including this, but the gating factor in this case is "how fast can you type?"...

So, what is the problem you are really trying to solve?

[Segfault]

SIGHUP will initiate graceful restart, meaning configuration files are re-read. Is this what you want?

[Segfault]

/proc/<PID>/cmdline

It's the command line right there, never tried to alter it.

Why don't you try and tell us?

[smolloy]

Thanks guys.

Segfault: I tried your suggestion, but it appears that file is unwriteable.

Maybe the guy who made the original comment was just lying?

[Cabhan]

procfs is for getting information about running processes. I believe that it is mostly read-only, and that you cannot modify processes through it. Indeed, according to the proc man page:

The proc filesystem is a pseudo-filesystem which is used as an interface to kernel data structures. It is commonly mounted at /proc. Most of it is read-only, but some files allow kernel variables to be changed.

Having said that, it is possible to modify running processes by using a system call called ptrace, which is how gdb works. ptrace allows you to access and modify the memory and registers of a running process. However, doing so meaningfully can be very difficult.

I cannot see the comment thread of the entry that you posted, but I've certainly never heard of modifying a process through procfs, and even doing so via ptrace would be quite difficult.