setmntent (3)

#include <stdio.h>
#include <mntent.h>

FILE *setmntent(const char *filename, const char *type);

struct mntent *getmntent(FILE *fp);

int addmntent(FILE *fp, const struct mntent *mnt);

int endmntent(FILE *fp);

char *hasmntopt(const struct mntent *mnt, const char *opt);

/* GNU extension */
#include <mntent.h>

struct mntent *getmntent_r(FILE *fp, struct mntent *mntbuf,
                           char *buf, int buflen);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getmntent_r(): _BSD_SOURCE || _SVID_SOURCE

These routines are used to access the filesystem description file /etc/fstab and the mounted filesystem description file /etc/mtab.

The setmntent() function opens the filesystem description file filename and returns a file pointer which can be used by getmntent(). The argument type is the type of access required and can take the same values as the mode argument of fopen(3).

The getmntent() function reads the next line from the filesystem description file fp and returns a pointer to a structure containing the broken out fields from a line in the file. The pointer points to a static area of memory which is overwritten by subsequent calls to getmntent().

The addmntent() function adds the mntent structure mnt to the end of the open file fp.

The endmntent() function closes the filesystem description file fp.

The hasmntopt() function scans the mnt_opts field (see below) of the mntent structure mnt for a substring that matches opt. See <mntent.h> and mount(8) for valid mount options.

The reentrant getmntent_r() function is similar to getmntent(), but stores the struct mount in the provided *mntbuf and stores the strings pointed to by the entries in that struct in the provided array buf of size buflen.

The mntent structure is defined in <mntent.h> as follows:

struct mntent {
    char *mnt_fsname;   /* name of mounted filesystem */
    char *mnt_dir;      /* filesystem path prefix */
    char *mnt_type;     /* mount type (see mntent.h) */
    char *mnt_opts;     /* mount options (see mntent.h) */
    int   mnt_freq;     /* dump frequency in days */
    int   mnt_passno;   /* pass number on parallel fsck */
};

Since fields in the mtab and fstab files are separated by whitespace, octal escapes are used to represent the four characters space (\040), tab (\011), newline (\012) and backslash (\134) in those files when they occur in one of the four strings in a mntent structure. The routines addmntent() and getmntent() will convert from string representation to escaped representation and back.

The getmntent() and getmntent_r() functions return a pointer to the mntent structure or NULL on failure.

The addmntent() function returns 0 on success and 1 on failure.

The endmntent() function always returns 1.

The hasmntopt() function returns the address of the substring if a match is found and NULL otherwise.

/etc/fstab          filesystem description file
/etc/mtab           mounted filesystem description file

The nonreentrant functions are from SunOS 4.1.3. A routine getmntent_r() was introduced in HP-UX 10, but it returns an int. The prototype shown above is glibc-only.

System V also has a getmntent() function but the calling sequence differs, and the returned structure is different. Under System V /etc/mnttab is used. 4.4BSD and Digital UNIX have a routine getmntinfo(), a wrapper around the system call getfsstat().

fopen(3), fstab(5), mount(8)

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