3 ms·

Can you show an example of how this would work with BASH_ARGV0?

chrisseaton 8y ago
Sorry I don’t know anything about how Bash is implemented, but when someone assigns to that variable Bash just needs to write that string to argv.
- dualbus 8y ago
  I tried python, bash and even C, none of them update /proc/self/comm when argv[0] is updated: dualbus@system76-pc:~$ cat argv0.c #include <stdio.h> #include <string.h> int main(int argc, char **argv) { FILE *fp; char buf[256]; // XXX :-) strcpy(argv[0], "XYZ"); //puts(argv[0]); fp = fopen("/proc/self/comm", "r"); fread(&buf, 1, 256, fp); buf[255] = '\0'; puts(buf); } dualbus@system76-pc:~$ gcc -o argv0 argv0.c -Wall dualbus@system76-pc:~$ ./argv0 argv0 dualbus@system76-pc:~$ python -c 'import sys; sys.argv[0] = "XYZ"; print(open("/proc/self/comm").read())' python dualbus@system76-pc:~$ ~/src/gnu/bash/bash -c 'BASH_ARGV0="XYZ"; cat /proc/$BASHPID/comm' bash Furthermore, https://github.com/torvalds/linux/blob/master/Documentation/filesystems/proc.txt#L1749 https://github.com/torvalds/linux/blob/master/Documentation/... says: > 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm > -------------------------------------------------------- > These files provide a method to access a tasks comm value. It also allows for > a task to set its own or one of its thread siblings comm value. The comm value > is limited in size compared to the cmdline value, so writing anything longer > then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated > comm value. Which works as advertised: dualbus@system76-pc:~$ ~/src/gnu/bash/bash -c 'echo -n XYZ > /proc/$BASHPID/comm; ps -p $BASHPID' PID TTY TIME CMD 28797 pts/6 00:00:00 XYZ Can you show me an example, in any language, where updating argv[0] causes ps (or /proc/self/comm) to show the updated value? EDIT: formatting. EDIT2: I stand corrected, see willglynn's comment.
  - LukeShu 8y ago
    You're looking at the wrong file. Setting argv[0] doesn't update /proc/self/comm, it updates /proc/self/cmdline. demo.c: #include <unistd.h> #include <string.h> int main(int argc, char *argv[]) { strcpy(argv[0], "frob"); sleep(100); } Terminal 1: $ make demo cc demo.c -o demo $ ./demo --greppable Terminal 2: $ ps aux|grep greppable luke 25858 0.0 0.0 2164 752 pts/0 S+ 00:32 0:00 frob o --greppable luke 25931 0.0 0.0 8192 2356 pts/5 S+ 00:32 0:00 grep --color=auto greppable $ cat -v /proc/25858/cmdline frob^@o^@--greppable^@$
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  - chrisseaton 8y ago
    $ ruby -e "\$0 = 'im not lying to you'; sleep" $ ps

Sorry I don’t know anything about how Bash is implemented, but when someone assigns to that variable Bash just needs to write that string to argv.

dualbus 8y ago
I tried python, bash and even C, none of them update /proc/self/comm when argv[0] is updated: dualbus@system76-pc:~$ cat argv0.c #include <stdio.h> #include <string.h> int main(int argc, char **argv) { FILE *fp; char buf[256]; // XXX :-) strcpy(argv[0], "XYZ"); //puts(argv[0]); fp = fopen("/proc/self/comm", "r"); fread(&buf, 1, 256, fp); buf[255] = '\0'; puts(buf); } dualbus@system76-pc:~$ gcc -o argv0 argv0.c -Wall dualbus@system76-pc:~$ ./argv0 argv0 dualbus@system76-pc:~$ python -c 'import sys; sys.argv[0] = "XYZ"; print(open("/proc/self/comm").read())' python dualbus@system76-pc:~$ ~/src/gnu/bash/bash -c 'BASH_ARGV0="XYZ"; cat /proc/$BASHPID/comm' bash Furthermore, https://github.com/torvalds/linux/blob/master/Documentation/filesystems/proc.txt#L1749 https://github.com/torvalds/linux/blob/master/Documentation/... says: > 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm > -------------------------------------------------------- > These files provide a method to access a tasks comm value. It also allows for > a task to set its own or one of its thread siblings comm value. The comm value > is limited in size compared to the cmdline value, so writing anything longer > then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated > comm value. Which works as advertised: dualbus@system76-pc:~$ ~/src/gnu/bash/bash -c 'echo -n XYZ > /proc/$BASHPID/comm; ps -p $BASHPID' PID TTY TIME CMD 28797 pts/6 00:00:00 XYZ Can you show me an example, in any language, where updating argv[0] causes ps (or /proc/self/comm) to show the updated value? EDIT: formatting. EDIT2: I stand corrected, see willglynn's comment.
- LukeShu 8y ago
  You're looking at the wrong file. Setting argv[0] doesn't update /proc/self/comm, it updates /proc/self/cmdline. demo.c: #include <unistd.h> #include <string.h> int main(int argc, char *argv[]) { strcpy(argv[0], "frob"); sleep(100); } Terminal 1: $ make demo cc demo.c -o demo $ ./demo --greppable Terminal 2: $ ps aux|grep greppable luke 25858 0.0 0.0 2164 752 pts/0 S+ 00:32 0:00 frob o --greppable luke 25931 0.0 0.0 8192 2356 pts/5 S+ 00:32 0:00 grep --color=auto greppable $ cat -v /proc/25858/cmdline frob^@o^@--greppable^@$
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- chrisseaton 8y ago
  $ ruby -e "\$0 = 'im not lying to you'; sleep" $ ps