[C] print a list of mounted filesystems

/* ch08-mounted.c --- print a list of mounted filesystems */

/* NOTE: GNU/Linux specific! */

#include <stdio.h>
#include <errno.h>
#include <mntent.h> /* for getmntent(), et al. */
#include <unistd.h> /* for getopt() */

void process(const char *filename);
void print_mount(const struct mntent *fs);

char *myname;

/* main --- process options */

int main(int argc, char **argv)
{
    int c;
    char *file = "/etc/mtab";   /* default file to read */

    myname = argv[0];
    while ((c = getopt(argc, argv, "f:")) != -1) {
        switch (c) {
        case 'f':
            file = optarg;
            break;
        default:
            fprintf(stderr, "usage: %s [-f fstab-file]\n", argv[0]);
            exit(1);
        }
    }

    process(file);
    return 0;
}

/* process --- read struct mntent structures from file */

void process(const char *filename)
{
    FILE *fp;
    struct mntent *fs;

    fp = setmntent(filename, "r");  /* read only */
    if (fp == NULL) {
        fprintf(stderr, "%s: %s: could not open: %s\n",
            myname, filename, strerror(errno));
        exit(1);
    }

    while ((fs = getmntent(fp)) != NULL)
        print_mount(fs);

    endmntent(fp);
}

/* print_mount --- print a single mount entry */

void print_mount(const struct mntent *fs)
{
    printf("%s %s %s %s %d %d\n",
        fs->mnt_fsname,
        fs->mnt_dir,
        fs->mnt_type,
        fs->mnt_opts,
        fs->mnt_freq,
        fs->mnt_passno);
}

Reference:

• Linux / Unix Command: setmntent