GETPWNAM(3C) Standard C Library Functions GETPWNAM(3C)


NAME


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 non-
reentrant 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:


+--------------------+------------------------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+------------------------------------------+
|Interface Stability | Committed |
+--------------------+------------------------------------------+
|MT-Level | See Reentrant Interfaces in DESCRIPTION. |
+--------------------+------------------------------------------+
|Standard | See below. |
+--------------------+------------------------------------------+


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. See nsswitch.conf(4).


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.


February 25, 2017 GETPWNAM(3C)