Is there any alternative API for getcwd to get the working direcory of process

Question

In our application we call getcwd(3) to get the current working directory.

When the process starts running, if anyone deletes the directory path, then the process is running but getcwd API fails (returns NULL).

Example: Process name is: a.exe present in /root/appl/a.exe after running a.exe, if the current working directory is deleted the getcwd(3) api fails.

Is there any alternative API for getcwd(3) to know the current working directory of a process, even if the directory path deleted?

What would expect to get back if the directory has been deleted? If you're running something as a daemon then you should probably `chdir("/");` almost immediately. — mu is too short, Jun 24 '11 at 06:18
the application is deployed by creating a temp directory, after appln start running the temp folder will be deleted... hence getcwd call fails.... I need to know is any other way to know the local directory of process...[for linux system] — Syedsma, Jun 24 '11 at 06:36
What do you want/expect to get back, when you're in an unlinked directory? It has no pathname! — Toby Speight, Aug 14 '19 at 16:32

score 4 · Answer 1 · edited May 23 '17 at 12:27

I'm not entirely sure what you will do with the results of the current working directory when the directory will continue to exist only as long as it is held open -- you can't create new files in the directory, and it had to be empty so it could be deleted -- but you can use readlink(2) on /proc/self/cwd to discover the name:

$ mkdir syedsma
$ cd syedsma/
$ /tmp/proccwd 
/proc/self/cwd reports: /tmp/syedsma
$ /tmp/getcwd 
getcwd: /tmp/syedsma
$ rmdir ../syedsma/
$ /tmp/getcwd
getcwd failed: No such file or directory
$ /tmp/proccwd 
/proc/self/cwd reports: /tmp/syedsma (deleted)
$

Here's my getcwd.c:

#include <stdio.h>
#include <unistd.h>

int main(int argc, char* argv[]) {
    char p[1000];
    char *r;
    r = getcwd(p, sizeof(p));
    if (!r)
        perror("getcwd failed");
    else
        printf("getcwd: %s\n", p);
    return 0;
}

And here's my proccwd.c:

#include <stdio.h>
#include <unistd.h>
#include <limits.h>

int main(int argc, char* argv[]) {
    char buf[PATH_MAX];

    ssize_t r = readlink("/proc/self/cwd", buf, sizeof(buf));

    if (r < 0) {
        perror("readlink /proc/self/cwd failed");
        return 1;
    } else {
        buf[PATH_MAX-1] = '\0';
        printf("/proc/self/cwd reports: %s\n", buf);
    }
    return 0;
}

mu is too short is correct with his advice to chdir("/"); if it is a daemon -- I can imagine that you might have a good reason for your program to otherwise know its current working directory, and even have an idea of what the pathname might have been if it did still exist -- but in general, you shouldn't care. The pathname "." will work in just about every case where it makes sense to need the current working directory, until you need to implement a pwd shell built-in for the user.

score 0 · Answer 2 · answered Jun 24 '11 at 06:42

Try this.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>

int main() {
  char path[256];
  char buf[BUFSIZ];

  mkdir("/tmp/foo", 0755);
  chdir("/tmp/foo");
  rmdir("/tmp/foo");

  sprintf(path, "/proc/%d/cwd", getpid());
  if (readlink(path, buf, sizeof(buf)) != -1) {
    char* stop = buf+strlen(buf)-10;
    if (!strcmp(stop, " (deleted)")) {
      *stop = 0;
    }
    printf("[%s]\n", buf);
  }
}

score 0 · Answer 3 · answered Jun 24 '11 at 07:27

0

get the $PWD environment variable and cache it in your application.

answered Jun 24 '11 at 07:27

balki

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Is there any alternative API for getcwd to get the working direcory of process

3 Answers3