Setting the Thread /Proc/Pid/Cmdline

Setting the thread /proc/PID/cmdline?

If you want to do this in a portable way, something that will work across multiple Unix variations, there are very few options available.

What you have to do is that your caller process must call exec with the argv [0] argument pointing to the name that you would like to see in the process output, and the filename pointing to the actual executable.

You can try this behavior from the shell by using:

exec -a "This is my cute name" bash

That will replace the current bash process with one named "This is my cute name".

For doing this in C, you can look at the source code of sendmail or any other piece of software that has been ported extensively and find all the variations that are needed across operating systems to support this.

Some operating systems have a setproctitle(3) API, some others allow you to override the contents of argv [0] and show that result.

parsing proc/pid/cmdline to get function parameters

All of the command line parameters (what would come through as the argv[] array) are actually null-separated strings in /proc/XXX/cmdline.

abatkin@penguin:~> hexdump -C /proc/28460/cmdline
00000000  70 65 72 6c 00 2d 65 00  31 20 77 68 69 6c 65 20  |perl.-e.1 while |
00000010  74 72 75 65 00                                    |true.|

This explains why when you cat'ed cmdline they were all "stuck" together (cat ignored the invalid NULL characters) and why your cout stopped after the first command line argument (the process name) since it thought that the process name was a null-terminated string and stopped looking for more characters at that point.

Processing Command Line Arguments

To process the command line arguments, you have a couple options. If you just want the entire command line as one giant string, loop from the 0 to (numRead - 2) (where numRead is the number of characters read) and replace any NULL bytes (curByte == 0) with spaces. Then just make sure to set the last character to be a NULL byte too (in case things got truncated due to the fixed-size buffer).

If you instead want an array with all of the arguments, you need to be more creative. One option would be to loop from 0 to (numRead - 1) and could all of the NULL bytes that you find. Then allocate an array of char*'s of that length. Then loop back through the command line, setting the beginning of every string (i.e. the first byte in the array, plus each byte following a NULL byte) to consecutive elements of the array of char*'s.

Just know that since you read to a fixed-size buffer, anything beyond that buffer would be truncated. So remember that whatever you do, you probably need to manually make sure that the end of the last string ends up being NULL terminated, otherwise most string handling functions won't know where the string ends and will keep on going forever.

Using prctl PR_SET_NAME to set name for process or thread?

Yes, you may use PR_SET_NAME in the first argument and the name as the second argument to set the name of the calling thread(or process). prctl returns 0 on success. Remember, it depends where you call this prctl. If you call it inside your process, it will change the name of that process and all of its belonging threads. If you call it inside a specific thread, it will change only the name of that thread.

Example:

int s;
s = prctl(PR_SET_NAME,"myProcess\0",NULL,NULL,NULL); // name: myProcess

Now, if you are running your process in Linux, type:

top

or

ps

To see the name attached to your process id.

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