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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



getspnam, getspnam_r, getspent, getspent_r, setspent, endspent, fgetspent, fgetspent_r - get password entry


#include <shadow.h>

struct spwd *getspnam(const char *name);
struct spwd *getspnam_r(const char *name, struct spwd *result,
     char *buffer, int buflen);
struct spwd *getspent(void);
struct spwd *getspent_r(struct spwd *result, char *buffer,
     int buflen);
void setspent(void);
void endspent(void);
struct spwd *fgetspent(FILE *fp);
struct spwd *fgetspent_r(FILE *fp, struct spwd *result,
     char *buffer, int buflen);


These functions are used to obtain shadow password entries. An entry may come from any of the sources for shadow specified in the /etc/nsswitch.conf file (see nsswitch.conf(5)).

The getspnam() function searches for a shadow password entry with the login name specified by the character string argument name.

The setspent(), getspent(), and endspent() functions are used to enumerate shadow password entries from the database.

The setspent() function sets (or resets) the enumeration to the beginning of the set of shadow password entries. This function should be called before the first call to getspent(). Calls to getspnam() leave the enumeration position in an indeterminate state.

Successive calls to getspent() return either successive entries or NULL, indicating the end of the enumeration.

The endspent() function may be called to indicate that the caller expects to do no further shadow password retrieval operations; the system may then close the shadow password file, deallocate resources it was using, and so forth. It is still allowed, but possibly less efficient, for the process to call more shadow password functions after calling endspent().

The fgetspent() function, unlike the other functions above, does not use nsswitch.conf; it reads and parses the next line from the stream fp, which is assumed to have the format of the shadow file (see shadow(5)).

Reentrant Interfaces

The getspnam(), getspent(), and fgetspent() functions use thread-specific data storage that is reused in each call to one of these functions by the same thread, making them safe to use but not recommended for multithreaded applications.

The getspnam_r(), getspent_r(), and fgetspent_r() functions provide reentrant interfaces for these operations.

Each reentrant interface performs the same operation as its non-reentrant counterpart, named by removing the _r suffix. The reentrant interfaces, however, use buffers supplied by the caller to store returned results, and are safe for use in both single-threaded and multithreaded applications.

Each reentrant interface takes the same argument as its non-reentrant counterpart, as well as the following additional arguments. The result argument must be a pointer to a struct spwd structure allocated by the caller. On successful completion, the function returns the shadow password entry in this structure. The buffer argument must be a pointer to a buffer supplied by the caller. This buffer is used as storage space for the shadow password data. All of the pointers within the returned struct spwd result point to data stored within this buffer (see RETURN VALUES). The buffer must be large enough to hold all of the data associated with the shadow password entry. The buflen argument should give the size in bytes of the buffer indicated by buffer.

For enumeration in multithreaded applications, the position within the enumeration is a process-wide property shared by all threads. The setspent() function may be used in a multithreaded application but resets the enumeration position for all threads. If multiple threads interleave calls to getspent_r(), the threads will enumerate disjoint subsets of the shadow password database.

Like its non-reentrant counterpart, getspnam_r() leaves the enumeration position in an indeterminate state.

Return Values

Password entries are represented by the struct spwd structure defined in <shadow.h>:

struct spwd{
    char           *sp_namp;     /* login name */
    char           *sp_pwdp;     /* encrypted passwd */
    int            sp_lstchg;    /* date of last change */
    int            sp_min;       /* min days to passwd change */
    int            sp_max;       /* max days to passwd change*/
    int            sp_warn;      /* warning period */
    int            sp_inact;     /* max days inactive */
    int            sp_expire;    /* account expiry date */
    unsigned int   sp_flag;      /* not used */

See shadow(5) for more information on the interpretation of this data.

The getspnam()and getspnam_r() functions each return a pointer to a struct spwd if they successfully locate the requested entry; otherwise they return NULL.

The getspent(), getspent_r(), fgetspent(), and fgetspent() functions each return a pointer to a struct spwd if they successfully enumerate an entry; otherwise they return NULL, indicating the end of the enumeration.

The getspnam(), getspent(), and fgetspent() functions use thread–specific data storage, so returned data must be copied before a subsequent call to any of these functions if the data is to be saved.

When the pointer returned by the reentrant functions getspnam_r(), getspent_r(), and fgetspent_r() is non-null, it is always equal to the result pointer that was supplied by the caller.


The reentrant functions getspnam_r(), getspent_r(), and fgetspent_r() will return NULL and set errno to ERANGE if the length of the buffer supplied by caller is not large enough to store the result. See Intro(2) for the proper usage and interpretation of errno in multithreaded applications.


See attributes(7) for descriptions of the following attributes:

See “Reentrant Interfaces” in DESCRIPTION.

See Also

passwd(1), yppasswd(1), getpwnam(3C), getlogin(3C), nsswitch.conf(5), passwd(5), shadow(5), attributes(7)


The reentrant interfaces getspnam_r(), getspent_r(), and fgetspent_r() are included in this release on an uncommitted basis only, and are subject to change or removal in future minor releases.


Use of the enumeration interfaces getspent() and getspent_r() is not recommended; enumeration is supported for the shadow file and NIS, but in general is not efficient and may not be supported for all database sources. The semantics of enumeration are discussed further in nsswitch.conf(5).

Access to shadow password information may be restricted in a manner depending on the database source being used. Access to the /etc/shadow file is generally restricted to processes running with the effective uid of the file owner or the {PRIV_FILE_DAC_READ} privilege. Other database sources may impose stronger or less stringent restrictions.

Empty fields in the database source return -1 values for all fields except sp_pwdp and sp_flag, where the value returned is 0.

When NIS is used as the database source, the information for the shadow password entries is obtained from the passwd.byname map. This map stores only the information for the sp_namp and sp_pwdp fields of the struct spwd structure. Shadow password entries obtained from NIS will contain the value –1 in the remainder of the fields.