поиск в базе данных пользователей по идентификатору пользователя (search user database for a user ID)
Пролог (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.
Имя (Name)
getpwuid, getpwuid_r — search user database for a user ID
Синопсис (Synopsis)
#include <pwd.h>
struct passwd *getpwuid(uid_t uid);
int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer,
size_t bufsize, struct passwd **result);
Описание (Description)
The getpwuid() function shall search the user database for an
entry with a matching uid.
The getpwuid() function need not be thread-safe.
Applications wishing to check for error situations should set
errno to 0 before calling getpwuid(). If getpwuid() returns a
null pointer and errno is set to non-zero, an error occurred.
The getpwuid_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 uid. 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.
Возвращаемое значение (Return value)
The getpwuid() 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.
If successful, the getpwuid_r() function shall return zero;
otherwise, an error number shall be returned to indicate the
error.
Ошибки (Error)
These functions may fail if:
EIO An I/O error has occurred.
EINTR A signal was caught during getpwuid().
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 getpwuid_r() function may fail if:
ERANGE Insufficient storage was supplied via buffer and bufsize
to contain the data to be referenced by the resulting
passwd structure.
The following sections are informative.
Примеры (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 getpwuid_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 = 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);
Getting an Entry for the Root User
The following example gets the user database entry for the user
with user ID 0 (root).
#include <sys/types.h>
#include <pwd.h>
...
uid_t id = 0;
struct passwd *pwd;
pwd = getpwuid(id);
Finding the Name for the Effective User ID
The following example defines pws as a pointer to a structure of
type passwd, which is used to store the structure pointer
returned by the call to the getpwuid() function. The geteuid()
function shall return the effective user ID of the calling
process; this is used as the search criteria for the getpwuid()
function. The call to getpwuid() shall return a pointer to the
structure containing that user ID value.
#include <unistd.h>
#include <sys/types.h>
#include <pwd.h>
...
struct passwd *pws;
pws = getpwuid(geteuid());
Finding an Entry in the User Database
The following example uses getpwuid() to search the user database
for a user ID that was previously stored in a 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.
#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);
Использование в приложениях (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 getpwuid_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.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
getpwnam(3p), geteuid(3p), getuid(3p), getlogin(3p), sysconf(3p)
The Base Definitions volume of POSIX.1‐2017, pwd.h(0p),
sys_types.h(0p)
