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getpwuid.3p (7621B)

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.TH GETPWUID "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
getpwuid,
getpwuid_r
\(em search user database for a user ID
.SH SYNOPSIS
.LP
.nf
#include <pwd.h>
.P
struct passwd *getpwuid(uid_t \fIuid\fP);
int getpwuid_r(uid_t \fIuid\fP, struct passwd *\fIpwd\fP, char *\fIbuffer\fP,
    size_t \fIbufsize\fP, struct passwd **\fIresult\fP);
.fi
.SH DESCRIPTION
The
\fIgetpwuid\fR()
function shall search the user database for an entry with a matching
.IR uid .
.P
The
\fIgetpwuid\fR()
function need not be thread-safe.
.P
Applications wishing to check for error situations should set
.IR errno
to 0 before calling
\fIgetpwuid\fR().
If
\fIgetpwuid\fR()
returns a null pointer and
.IR errno
is set to non-zero, an error occurred.
.P
The
\fIgetpwuid_r\fR()
function shall update the
.BR passwd
structure pointed to by
.IR pwd
and store a pointer to that structure at the location pointed to by
.IR result .
The structure shall contain an entry from the user database with a
matching
.IR uid .
Storage referenced by the structure is allocated from the memory
provided with the
.IR buffer
parameter, which is
.IR bufsize
bytes in size. A call to
.IR sysconf (_SC_GETPW_R_SIZE_MAX)
returns either \-1 without changing
.IR errno
or an initial value suggested for the size of this buffer.
A null pointer shall be returned at the location pointed to by
.IR result
on error or if the requested entry is not found.
.SH "RETURN VALUE"
The
\fIgetpwuid\fR()
function shall return a pointer to a
.BR "struct passwd"
with the structure as defined in
.IR <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,
.IR errno
shall not be changed. On error,
.IR errno
shall be set to indicate the error.
.P
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
\fIgetpwent\fR(),
\fIgetpwnam\fR(),
or
\fIgetpwuid\fR().
The returned pointer, and pointers within the structure, might also
be invalidated if the calling thread is terminated.
.P
If successful, the
\fIgetpwuid_r\fR()
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
These functions may fail if:
.TP
.BR EIO
An I/O error has occurred.
.TP
.BR EINTR
A signal was caught during
\fIgetpwuid\fR().
.TP
.BR EMFILE
All file descriptors available to the process are currently open.
.TP
.BR ENFILE
The maximum allowable number of files is currently open in the system.
.P
The
\fIgetpwuid_r\fR()
function may fail if:
.TP
.BR ERANGE
Insufficient storage was supplied via
.IR buffer
and
.IR bufsize
to contain the data to be referenced by the resulting
.BR passwd
structure.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
Note that
.IR 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
\fIgetpwuid_r\fR().
.sp
.RS 4
.nf
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 = getpwuid_r(42, &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);
.fi
.P
.RE
.SS "Getting an Entry for the Root User"
.P
The following example gets the user database entry for the user with
user ID 0 (root).
.sp
.RS 4
.nf
#include <sys/types.h>
#include <pwd.h>
\&...
uid_t id = 0;
struct passwd *pwd;
.P
pwd = getpwuid(id);
.fi
.P
.RE
.SS "Finding the Name for the Effective User ID"
.P
The following example defines
.IR pws
as a pointer to a structure of type
.BR passwd ,
which is used to store the structure pointer returned by the call to
the
\fIgetpwuid\fR()
function. The
\fIgeteuid\fR()
function shall return the effective user ID of the calling process;
this is used as the search criteria for the
\fIgetpwuid\fR()
function. The call to
\fIgetpwuid\fR()
shall return a pointer to the structure containing that user ID value.
.sp
.RS 4
.nf
#include <unistd.h>
#include <sys/types.h>
#include <pwd.h>
\&...
struct passwd *pws;
pws = getpwuid(geteuid());
.fi
.P
.RE
.SS "Finding an Entry in the User Database"
.P
The following example uses
\fIgetpwuid\fR()
to search the user database for a user ID that was previously stored in
a
.BR stat
structure, then prints out the user name if it is found. If the user
is not found, the program prints the numeric value of the user ID for
the entry.
.sp
.RS 4
.nf
#include <sys/types.h>
#include <pwd.h>
#include <stdio.h>
\&...
struct stat statbuf;
struct passwd *pwd;
\&...
if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
    printf(" %-8.8s", pwd->pw_name);
else
    printf(" %-8d", statbuf.st_uid);
.fi
.P
.RE
.SH "APPLICATION USAGE"
Three names associated with the current process can be determined:
.IR getpwuid (\c
\fIgeteuid\fR())
returns the name associated with the effective user ID of the process;
\fIgetlogin\fR()
returns the name associated with the current login activity; and
.IR getpwuid (\c
\fIgetuid\fR())
returns the name associated with the real user ID of the process.
.P
The
\fIgetpwuid_r\fR()
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.
.P
Portable applications should take into account that it is usual
for an implementation to return \-1 from
\fIsysconf\fR()
indicating that there is no maximum for _SC_GETPW_R_SIZE_MAX.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIgetpwnam\fR\^(\|)",
.IR "\fIgeteuid\fR\^(\|)",
.IR "\fIgetuid\fR\^(\|)",
.IR "\fIgetlogin\fR\^(\|)",
.IR "\fIsysconf\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<pwd.h>\fP",
.IR "\fB<sys_types.h>\fP"
.\"
.SH 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 .
.PP
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 .