ENDPWENT(3P)

💖 ENDPWENT(3P) — the user database girlies 💖

okay so bestie, this is endpwent(3P) from the POSIX Programmer's Manual. yes, that POSIX. the one with the 2017 energy. sit down, hydrate, we're talking about the user database.

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✨ PROLOG ✨

real talk before we start: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so pls consult the corresponding Linux manual page for details of Linux behavior), or the interface may literally not be implemented on Linux at all. 😭 not me warning you first thing.

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🎀 NAME 🎀

endpwent, getpwent, setpwent — user database functions. the holy trinity of "who even is this user". 👑

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🦋 SYNOPSIS 🦋

#include <pwd.h>

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

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🌸 DESCRIPTION 🌸

These functions shall retrieve information about users. yes, like, actual humans. in a database. it's giving census but make it C. 💅

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. If the user database is not already open, getpwent() shall open it and return a pointer to a passwd structure containing the first entry in the 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. it's a lil iterator bestie, one entry at a time, main character energy per call. ✨

If an end-of-file or an error is encountered on reading, getpwent() shall return a null pointer. 😔 that's it, that's the end of the list.

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. so like… sometimes the system is gatekeeping and you just have to accept it. 🙈

The setpwent() function shall rewind the user database so that the next getpwent() call returns the first entry, allowing repeated searches. it's the "rewind the tape" button. ⏪

The endpwent() function shall close the user database. clean up after yourself, queen. 🧚

The setpwent() and endpwent() functions shall not change the setting of errno if successful. noted.

On error, the setpwent() and endpwent() functions shall set errno to indicate the error.

Since no value is returned by the setpwent() and endpwent() functions, an application wishing to check for error situations should set errno to 0, then call the function, then check errno. yes this is the ritual. do the ritual. 🔮

These functions need not be thread-safe. 🫶 just so you know. not thread-safe, and that's on purpose.

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💜 RETURN VALUE 💜

On successful completion, getpwent() shall return a pointer to a passwd structure. slay.

On end-of-file, getpwent() shall return a null pointer and shall not change the setting of errno. (important distinction bestie, write it down.)

On error, getpwent() shall return a null pointer and 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. Do not touch. Hands off. It is not yours. 🙅

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(). The returned pointer, and pointers within the structure, might also be invalidated if the calling thread is terminated. so yeah, that pointer is on borrowed time fr fr. 💀

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🔥 ERRORS 🔥

These functions may fail if:

• EINTR — a signal was caught during the operation. rude of it tbh.
• EIO — an I/O error has occurred. the disk said no. 😭

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

• EMFILE — all file descriptors available to the process are currently open. every single one. no crumbs left.
• ENFILE — the maximum allowable number of files is currently open in the system. the whole system is full bestie.

The following sections are informative. (yes that means they're the lil bonus lore sections. keep reading.) ✨

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🍓 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. iconic behavior honestly.

#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();
}

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👑 APPLICATION USAGE 👑

These functions are provided due to their historical usage. (it's giving legacy code, it's giving "we keep it because grandma wrote it".) 🫶

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. like, do not assume the layout, bestie. it can move. it can be a whole different thing.

Applications should use getpwuid() whenever possible because it avoids these dependencies. that's the recommendation. that's the tea. ☕

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💅 RATIONALE 💅

None.

(i know. nothing. the void. the silence. we move.) 💀

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⭐ FUTURE DIRECTIONS ⭐

None.

(again, nothing. the future is blank and unbothered.) ✨

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🌟 SEE ALSO 🌟

• endgrent()
• getlogin()
• getpwnam()
• getpwuid()

The Base Definitions volume of POSIX.1‐2017, <pwd.h>

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🎀 COPYRIGHT 🎀

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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okay that's the whole page bestie, you ate it, you read it, you understood it 💖 this was brought to you by IEEE/The Open Group, dated 2017, and the page itself is ENDPWENT(3P). now go call endpwent() and close that database, you deserve the rest. 🦋✨