NAME

getpwnam, getpwnam_r — search user database for a name

SYNOPSIS

#include <pwd.h>

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


DESCRIPTION

The getpwnam() function shall search the user database for an entry with a matching name.

The getpwnam() function need not be thread-safe.

Applications wishing to check for error situations should set errno to 0 before calling getpwnam(). If getpwnam() returns a null pointer and errno is non-zero, an error occurred.

The getpwnam_r() function shall update the passwd structure pointed to by pwd and store a pointer to that structure at the location pointed to by result. The structure shall contain an entry from the user database with a matching name. Storage referenced by the structure is allocated from the memory provided with the buffer parameter, which is bufsize bytes in size. A call to sysconf(_SC_GETPW_R_SIZE_MAX) returns either -1 without changing errno or an initial value suggested for the size of this buffer. A null pointer shall be returned at the location pointed to by result on error or if the requested entry is not found.

RETURN VALUE

The getpwnam() function shall return a pointer to a struct passwd with the structure as defined in <pwd.h> with a matching entry if found. A null pointer shall be returned if the requested entry is not found, or an error occurs. If the requested entry was not found, errno shall not be changed. On error, errno shall be set to indicate the error.

The application shall not modify the structure to which the return value points, nor any storage areas pointed to by pointers within the structure. The returned pointer, and pointers within the structure, might be invalidated or the structure or the storage areas might be overwritten by a subsequent call to getpwent(), getpwnam(), or getpwuid(). The returned pointer, and pointers within the structure, might also be invalidated if the calling thread is terminated.

The getpwnam_r() function shall return zero on success or if the requested entry was not found and no error has occurred. If an error has occurred, an error number shall be returned to indicate the error.

ERRORS

These functions may fail if:

[EIO]

An I/O error has occurred.

[EINTR]

A signal was caught during getpwnam().

[EMFILE]

All file descriptors available to the process are currently open.

[ENFILE]

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

The getpwnam_r() function shall fail if:

[ERANGE]

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

EXAMPLES

Note that sysconf(_SC_GETPW_R_SIZE_MAX) may return -1 if there is no hard limit on the size of the buffer needed to store all the groups returned. This example shows how an application can allocate a buffer of sufficient size to work with getpwnam_r().

long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
size_t len;
if (initlen == -1)
    /* Default initial length. */
    len = 1024;
else
    len = (size_t) initlen;
struct passwd result;
struct passwd *resultp;
char *buffer = malloc(len);
if (buffer == NULL)
    ...handle error...
int e;
while ((e = getpwnam_r("someuser", &result, buffer, len, &resultp))
        == ERANGE)
    {
    size_t newlen = 2 * len;
    if (newlen < len)
        ...handle error...
    len = newlen;
    char *newbuffer = realloc(buffer, len);
    if (newbuffer == NULL)
        ...handle error...
    buffer = newbuffer;
    }
if (e != 0)
    ...handle error...
free (buffer);

Getting an Entry for the Login Name

The following example uses the getlogin() function to return the name of the user who logged in; this information is passed to the getpwnam() function to get the user database entry for that user.

#include <sys/types.h>
#include <pwd.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
...
char *lgn;
struct passwd *pw;
...
if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
    fprintf(stderr, "Get of user information failed.\n"); exit(1);
}
...

APPLICATION 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.

The getpwnam_r() function is thread-safe and returns values in a user-supplied buffer instead of possibly using a static data area that may be overwritten by each call.

Portable applications should take into account that it is usual for an implementation to return -1 from sysconf() indicating that there is no maximum for _SC_GETPW_R_SIZE_MAX.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

getpwuid, sysconf

XBD <pwd.h>, <sys/types.h>

CHANGE HISTORY

First released in Issue 1. Derived from System V Release 2.0.

Issue 5

Normative text previously in the APPLICATION USAGE section is moved to the RETURN VALUE section.

The getpwnam_r() function is included for alignment with the POSIX Threads Extension.

A note indicating that the getpwnam() function need not be reentrant is added to the DESCRIPTION.

Issue 6

The getpwnam_r() function is marked as part of the Thread-Safe Functions option.

The Open Group Corrigendum U028/3 is applied, correcting text in the DESCRIPTION describing matching the name.

In the SYNOPSIS, the optional include of the <sys/types.h> header is removed.

In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

• The requirement to include <sys/types.h> has been removed. Although <sys/types.h> was required for conforming implementations of previous POSIX specifications, it was not required for UNIX applications.

• In the RETURN VALUE section, the requirement to set errno on error is added.

• The [EMFILE], [ENFILE], and [ENXIO] optional error conditions are added.

The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a static data area.

IEEE PASC Interpretation 1003.1 #116 is applied, changing the description of the size of the buffer from bufsize characters to bytes.

Issue 7

Austin Group Interpretation 1003.1-2001 #156 is applied.

SD5-XBD-ERN-4 is applied, changing the definition of the [EMFILE] error.

SD5-XSH-ERN-166 is applied.

The getpwnam_r() function is moved from the Thread-Safe Functions option to the Base.

A minor addition is made to the EXAMPLES section, reminding the application developer to free memory allocated as if by malloc().

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0255 [75,428] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0170 [808] and XSH/TC2-2008/0171 [656] are applied.

Issue 8

Austin Group Defect 398 is applied, changing the [ERANGE] error from "may fail" to "shall fail".

Austin Group Defect 1570 is applied, removing extra spacing in "==".