endpwent man page

Prolog

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endpwent, getpwent, setpwent — user database functions

Synopsis

#include <pwd.h>

void endpwent(void);
struct passwd *getpwent(void);
void setpwent(void);

Description

These functions shall retrieve information about users.

The getpwent() function shall return a pointer to a structure containing the broken-out fields of an entry in the user database. Each entry in the user database contains a passwd structure. When first called, getpwent() shall return a pointer to a passwd structure containing the first entry in the user database. Thereafter, it shall return a pointer to a passwd structure containing the next entry in the user database. Successive calls can be used to search the entire user database.

If an end-of-file or an error is encountered on reading, getpwent() shall return a null pointer.

An implementation that provides extended security controls may impose further implementation-defined restrictions on accessing the user database. In particular, the system may deny the existence of some or all of the user database entries associated with users other than the caller.

The setpwent() function effectively rewinds the user database to allow repeated searches.

The endpwent() function may be called to close the user database when processing is complete.

These functions need not be thread-safe.

Return Value

The getpwent() function shall return a null pointer on end-of-file or 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 getpwuid(), getpwnam(), or getpwent().

Errors

These functions may fail if:

EIO
An I/O error has occurred.

In addition, getpwent() and setpwent() may fail if:

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 following sections are informative.

Examples

Searching the User Database

The following example uses the getpwent() function to get successive entries in the user database, returning a pointer to a passwd structure that contains information about each user. The call to endpwent() closes the user database and cleans up.

#include <pwd.h>
#include <stdio.h>

void printname(uid_t uid)
{
    struct passwd *pwd;

    setpwent();
    while((pwd = getpwent()) != NULL) {
        if (pwd->pw_uid == uid) {
            printf("name=%s\n",pwd->pw_name);
            break;
        }
    }
    endpwent();
}

Application Usage

These functions are provided due to their historical usage. Applications should avoid dependencies on fields in the password database, whether the database is a single file, or where in the file system name space the database resides. Applications should use getpwuid() whenever possible because it avoids these dependencies.

See Also

endgrent(), getlogin(), getpwnam(), getpwuid()

The Base Definitions volume of POSIX.1‐2008, <pwd.h>

Info

2013 IEEE/The Open Group POSIX Programmer's Manual