在/ proc / pid / stat中使用文件名的奇怪行为

Question

I have a weird behavior with the value of filename in /proc/pid/stat.

My program's name is "test_dev", and when I execute it with "./test_dev" and i look on /proc/pid/stat, i see "pid (test) ....". Same in /proc/pid/status.

I change "test_dev" to "testdev" to see if the underscore is the culprit of this mess, but the same thing appear again.

I printf argv[0], and I correctly see "test_dev" (or "testdev").

I wonder how the field in stat is set, and why it's incomplet, because the man of /proc say that is the filename of the executable.

I think a little, and I wonder if Eclipse can be the culprit. This EDI gave me some surprise sometimes, and I won't be surprised if this is the case again, even if it really bug me that argv[0] and /proc/pid/stat have not the same value.

Is somebody have an explanation ?

thanks.

Answer 1

However, the real filename without "_dev" is 15 character long, and the "comm" field seem to be limited by the kernel to 15 character long ... So, the filename is truncated in /proc/pid/stat, … Where can I find this kind of documentation ?

Unfortunately, this seems to be not well documented where one would expect it, but there are some hints here and there on the proc man page.

/proc/[pid]/comm (since Linux 2.6.33)
              …  Strings longer than (16) characters are silently truncated.

/proc/[pid]/stat
              Status information about the process.  This is used by ps(1).
              It is defined in the kernel source file fs/proc/array.c.

TASK_COMM_LEN and the task_struct are defined in include/linux/sched.h :

#define TASK_COMM_LEN           16
…
struct task_struct {
…
    char                comm[TASK_COMM_LEN];

The difference between the 15 characters you observe and the 16 here is due to the terminating '\\0' .

Answer 2

The field in /proc/pid/stat you mention does not show argv[0], but the executed command. Probably, eclipse compiles the file to an executable named "test" and executes it.

This example:

execl("foo", "bar", "baz", NULL);

has a comm of "foo" (the thing in /proc/pid/stat), an argv[0] of "bar" and "baz" as argv[1]

To double-check that, you might try to call your program "xxxxx" and see, if it is still named "test" in /proc/pid/stat