getpwnam

, getpwnam_r

, getpwent

, getpwent_r

, getpwuid

, getpwuid_r

, setpwent

, endpwent

, fgetpwent

, fgetpwent_r

- get password entry

Synopsis

#include <pwd.h>

struct passwd *getpwnam(const char *name);

struct passwd *getpwnam_r(const char *name, struct passwd *pwd,
     char *buffer, int buflen);

struct passwd *getpwent(void);

struct passwd *getpwent_r(struct passwd *pwd, char *buffer,
     int buflen);

struct passwd *getpwuid(uid_t uid);

struct passwd *getpwuid_r(uid_t uid, struct passwd *pwd,
    char *buffer, int  buflen);

void setpwent(void);

void endpwent(void);

struct passwd *fgetpwent(FILE *f);

struct passwd *fgetpwent_r(FILE *f, struct passwd *pwd,
     char *buffer, int buflen);

Standard conforming

cc [ flag...] file... -D_POSIX_PTHREAD_SEMANTICS [ library... ]

int getpwnam_r(const char *name, struct passwd *pwd, char *buffer,
     size_t bufsize, struct passwd **result);

int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer,
     size_t bufsize, struct passwd **result);

Description

These functions are used to obtain password entries. Entries can come from any of the sources for passwd specified in the /etc/nsswitch.conf file (see nsswitch.conf(4)).

The getpwnam() function searches for a password entry with the login name specified by the character string parameter name.

The getpwuid() function searches for a password entry with the (numeric) user ID specified by the uid parameter.

The setpwent(), getpwent(), and endpwent() functions are used to enumerate password entries from the database. The setpwent() function sets (or resets) the enumeration to the beginning of the set of password entries. This function should be called before the first call to getpwent(). Calls to getpwnam() and getpwuid() leave the enumeration position in an indeterminate state. Successive calls to getpwent() return either successive entries or a null pointer, indicating the end of the enumeration.

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

The fgetpwent() function, unlike the other functions above, does not use nsswitch.conf but reads and parses the next line from the stream f, which is assumed to have the format of the passwd file. See passwd(4).

Reentrant Interfaces

The getpwnam(), getpwuid(), getpwent(), and fgetpwent() 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 parallel functions getpwnam_r(), getpwuid_r(), getpwent_r(), and fgetpwent_r() 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 instead of using thread-specific data that can be overwritten by each call. They are safe for use in both single-threaded and multithreaded applications.

Each reentrant interface takes the same parameters as its non-reentrant counterpart, as well as the following additional parameters. The pwd parameter must be a pointer to a struct passwd structure allocated by the caller. On successful completion, the function returns the password entry in this structure. The parameter buffer is a pointer to a buffer supplied by the caller, used as storage space for the password data. All pointers within the returned struct passwd pwd point to data stored within this buffer; see passwd Structure below. The buffer must be large enough to hold all the data associated with the password entry. The parameter buflen (or bufsize for the standard-conforming versions; see standards(5)) should give the size in bytes of buffer. The maximum size needed for this buffer can be determined with the {_SC_GETPW_R_SIZE_MAX} sysconf(3C) parameter. The standard-conforming versions place a pointer to the modified pwd structure in the result parameter, instead of returning a pointer to this structure. A null pointer is returned at the location pointed to by result on error or if the requested entry is not found.

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

Like their non-reentrant counterparts, getpwnam_r() and getpwuid_r() leave the enumeration position in an indeterminate state.

passwd Structure

Password entries are represented by the struct passwd structure defined in <pwd.h>:

struct passwd {
    char *pw_name;      /* user's login name */
    char *pw_passwd;    /* no longer used */
    uid_t pw_uid;       /* user's uid */
    gid_t pw_gid;       /* user's gid */
    char *pw_age;       /* not used */
    char *pw_comment;   /* not used */
    char *pw_gecos;     /* typically user's full name */
    char *pw_dir;       /* user's home dir */
    char *pw_shell;     /* user's login shell */
};

The pw_passwd member should not be used as the encrypted password for the user; use getspnam() or getspnam_r() instead. See getspnam(3C).

Return Values

The getpwnam(), getpwnam_r(), getpwuid(), and getpwuid_r() functions each return a pointer to a struct passwd if they successfully locate the requested entry. A null pointer is returned if the requested entry is not found, or an error occurs. On error, errno is set to indicate the error.

Applications wishing to check for error situations should set errno to 0 before calling getpwnam(), getpwnam_r(), getpwuid(), getpwuid_r(), getpwent(), getpwent_r(), fgetpwent(), and fgetpwent_r(). If these functions return a null pointer and errno is non-zero, an error occurred.

The standard-conforming functions getpwnam_r() and getpwuid_r() can return 0 even on an error, particularly in the case where the requested entry is not found. The application needs to check the return value and that the pwd pointer is non-null. Otherwise, an error value is returned to indicate the error.

The getpwent(), getpwent_r(), fgetpwent(), and fgetpwent_r() functions each return a pointer to a struct passwd if they successfully enumerate an entry; otherwise they return a null pointer on end-of-file or error. On error, errno is set to indicate the error.

See Intro(2) for the proper usage and interpretation of errno in multithreaded applications.

The getpwnam(), getpwuid(), getpwent(), and fgetpwent() 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 getpwnam_r(), getpwuid_r(), getpwent_r(), and fgetpwent_r() is non-null, it is always equal to the pwd pointer that was supplied by the caller.

Errors

The getpwent_r(), fgetpwent(), and fgetpwent_r() functions will fail if:

EIO

An I/O error has occurred.

ERANGE

Insufficient storage was supplied by buffer and bufsize to contain the data to be referenced by the resulting passwd structure.

The getpwent_r() function will fail if:

EMFILE

There are {OPEN_MAX} file descriptors currently open in the calling process.

ENFILE

The maximum allowable number of files is currently open in the system.

The getpwnam(), getpwnam_r(), getpwuid(), getpwuid_r(), getpwent(), setpwent(), and endpwent() functions may fail if:

EIO

An I/O error has occurred.

The getpwnam(), getpwnam_r(), getpwuid(), getpwuid_r(), getpwent(), and setpwent() functions may fail if:

EMFILE

There are {OPEN_MAX} file descriptors currently open in the calling process.

ENFILE

The maximum allowable number of files is currently open in the system.

The getpwnam(), getpwnam_r(), getpwuid(), and getpwuid_r() functions may fail if:

EINTR

A signal was caught during the execution of the function call.

The getpwnam_r() and getpwuid_r() functions may fail if:

ERANGE

Insufficient storage was supplied by buffer and bufsize to contain the data to be referenced by the resulting passwd structure.

Usage

Three names associated with the current process can be determined: getpwuid(geteuid()) returns the name associated with the effective user ID of the process; getlogin() returns the name associated with the current login activity; and getpwuid(getuid()) returns the name associated with the real user ID of the process.

Attributes

See attributes(5) for descriptions of the following attributes:

For endpwent(), getpwent(), getpwnam(), getpwnam_r(), getpwuid(), getpwuid_r(), and setpwent(), see standards(5).

See Also

passwd(1), yppasswd(1), Intro(2), Intro(3), cuserid(3C), getgrnam(3C), getlogin(3C), getspnam(3C), nsswitch.conf(4), passwd(4), shadow(4), attributes(5), standards(5)

Notes

When compiling multithreaded programs, see Intro(3).

Use of the enumeration interfaces getpwent() and getpwent_r() is discouraged; enumeration is supported for the passwd file and NIS, but in general is not efficient and might not be supported for all database sources. The semantics of enumeration are discussed further in nsswitch.conf(4).

Previous releases allowed the use of `+' and `-' entries in /etc/passwd to selectively include and exclude NIS entries. The primary usage of these `+/-' entries is superseded by the name service switch, so the `+/-' form might not be supported in future releases.

If required, the `+/-' functionality can still be obtained for NIS by specifying compat as the source for passwd.

If the `+/-' is used, both /etc/shadow and /etc/passwd should have the same `+' and `-' entries to ensure consistency between the password and shadow databases.

If a password entry from any of the sources contains an empty uid or gid field, that entry will be ignored by the files and NIS name service switch backends, causing the user to appear unknown to the system.

If a password entry contains an empty gecos, home directory, or shell field, getpwnam() and getpwnam_r() return a pointer to a null string in the respective field of the passwd structure.

If the shell field is empty, login(1) automatically assigns the default shell. See login(1).

Solaris 2.4 and earlier releases provided definitions of the getpwnam_r() and getpwuid_r() functions as specified in POSIX.1c Draft 6. The final POSIX.1c standard changed the interface for these functions. Support for the Draft 6 interface is provided for compatibility only and might not be supported in future releases. New applications and libraries should use the standard-conforming interface.

For POSIX.1c-conforming applications, the _POSIX_PTHREAD_SEMANTICS and _REENTRANT flags are automatically turned on by defining the _POSIX_C_SOURCE flag with a value ≥199506L.