getspnam(3) - Linux manual page

getspnam(3) - Linux manual page
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getspnam(3) — Linux manual page
NAME
LIBRARY
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
FILES
ATTRIBUTES
VERSIONS
STANDARDS
SEE ALSO
COLOPHON
getspnam
(3) Library Functions Manual
getspnam
(3)
NAME
top
getspnam, getspnam_r, getspent, getspent_r, setspent, endspent,
fgetspent, fgetspent_r, sgetspent, sgetspent_r, putspent, lckpwdf,
ulckpwdf - get shadow password file entry
LIBRARY
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Standard C library (
libc
-lc
SYNOPSIS
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/* General shadow password file API */
#include
struct spwd *getspnam(const char *
name
);
struct spwd *getspent(void);
void setspent(void);
void endspent(void);
struct spwd *fgetspent(FILE *
stream
);
struct spwd *sgetspent(const char *
);
int putspent(const struct spwd *
, FILE *
stream
);
int lckpwdf(void);
int ulckpwdf(void);
/* GNU extension */
#include
int getspent_r(
size_t size;
struct spwd *
spbuf
char
buf
size
], size_t
size
struct spwd **
spbufp
);
int getspnam_r(
size_t size;
const char *
name
, struct spwd *
spbuf
char
buf
size
], size_t
size
struct spwd **
spbufp
);
int fgetspent_r(
size_t size;
FILE *
stream
, struct spwd *
spbuf
char
buf
size
], size_t
size
struct spwd **
spbufp
);
int sgetspent_r(
size_t size;
const char *
, struct spwd *
spbuf
char
buf
size
], size_t
size
struct spwd **
spbufp
);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)
):
getspent_r
(),
getspnam_r
(),
fgetspent_r
(),
sgetspent_r
():
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
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Long ago it was considered safe to have encrypted passwords openly
visible in the password file. When computers got faster and
people got more security-conscious, this was no longer acceptable.
Julianne Frances Haugh implemented the shadow password suite that
keeps the encrypted passwords in the shadow password database
(e.g., the local shadow password file
/etc/shadow
, NIS, and LDAP),
readable only by root.

The functions described below resemble those for the traditional
password database (e.g., see
getpwnam(3)
and
getpwent(3)
).

The
getspnam
() function returns a pointer to a structure
containing the broken-out fields of the record in the shadow
password database that matches the username
name

The
getspent
() function returns a pointer to the next entry in the
shadow password database. The position in the input stream is
initialized by
setspent
(). When done reading, the program may
call
endspent
() so that resources can be deallocated.

The
fgetspent
() function is similar to
getspent
() but uses the
supplied stream instead of the one implicitly opened by
setspent
().

The
sgetspent
() function parses the supplied string
into a
struct
spwd

The
putspent
() function writes the contents of the supplied struct
spwd *p
as a text line in the shadow password file format to
stream
. String entries with value NULL and numerical entries with
value -1 are written as an empty string.

The
lckpwdf
() function is intended to protect against multiple
simultaneous accesses of the shadow password database. It tries
to acquire a lock, and returns 0 on success, or -1 on failure
(lock not obtained within 15 seconds). The
ulckpwdf
() function
releases the lock again. Note that there is no protection against
direct access of the shadow password file. Only programs that use
lckpwdf
() will notice the lock.

These were the functions that formed the original shadow API.
They are widely available.
Reentrant versions
Analogous to the reentrant functions for the password database,
glibc also has reentrant functions for the shadow password
database. The
getspnam_r
() function is like
getspnam
() but stores
the retrieved shadow password structure in the space pointed to by
spbuf
. This shadow password structure contains pointers to
strings, and these strings are stored in the buffer
buf
of size
size
. A pointer to the result (in case of success) or NULL (in
case no entry was found or an error occurred) is stored in
*spbufp

The functions
getspent_r
(),
fgetspent_r
(), and
sgetspent_r
() are
similarly analogous to their nonreentrant counterparts.

Some non-glibc systems also have functions with these names, often
with different prototypes.
Structure
The shadow password structure is defined in

as follows:

struct spwd {
char *sp_namp; /* Login name */
char *sp_pwdp; /* Encrypted password */
long sp_lstchg; /* Date of last change
(measured in days since
1970-01-01 00:00:00 +0000 (UTC)) */
long sp_min; /* Min # of days between changes */
long sp_max; /* Max # of days between changes */
long sp_warn; /* # of days before password expires
to warn user to change it */
long sp_inact; /* # of days after password expires
until account is disabled */
long sp_expire; /* Date when account expires
(measured in days since
1970-01-01 00:00:00 +0000 (UTC)) */
unsigned long sp_flag; /* Reserved */
};
RETURN VALUE
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The functions that return a pointer return NULL if no more entries
are available or if an error occurs during processing. The
functions which have
int
as the return value return 0 for success
and -1 for failure, with
errno
set to indicate the error.

For the nonreentrant functions, the return value may point to
static area, and may be overwritten by subsequent calls to these
functions.

The reentrant functions return zero on success. In case of error,
an error number is returned.
ERRORS
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EACCES
The caller does not have permission to access the shadow
password file.
ERANGE
Supplied buffer is too small.
FILES
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/etc/shadow
local shadow password database file
/etc/.pwd.lock
lock file

The include file

defines the constant
_PATH_SHADOW
to
the pathname of the shadow password file.
ATTRIBUTES
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For an explanation of the terms used in this section, see
attributes(7)
┌───────────────┬───────────────┬────────────────────────────────┐
Interface
Attribute
Value
├───────────────┼───────────────┼────────────────────────────────┤
getspnam
() │ Thread safety │ MT-Unsafe race:getspnam locale │
├───────────────┼───────────────┼────────────────────────────────┤
getspent
() │ Thread safety │ MT-Unsafe race:getspent │
│ │ │ race:spentbuf locale │
├───────────────┼───────────────┼────────────────────────────────┤
setspent
(), │ Thread safety │ MT-Unsafe race:getspent locale │
endspent
(), │ │ │
getspent_r
() │ │ │
├───────────────┼───────────────┼────────────────────────────────┤
fgetspent
() │ Thread safety │ MT-Unsafe race:fgetspent │
├───────────────┼───────────────┼────────────────────────────────┤
sgetspent
() │ Thread safety │ MT-Unsafe race:sgetspent │
├───────────────┼───────────────┼────────────────────────────────┤
putspent
(), │ Thread safety │ MT-Safe locale │
getspnam_r
(), │ │ │
sgetspent_r
() │ │ │
├───────────────┼───────────────┼────────────────────────────────┤
lckpwdf
(), │ Thread safety │ MT-Safe │
ulckpwdf
(), │ │ │
fgetspent_r
() │ │ │
└───────────────┴───────────────┴────────────────────────────────┘

In the above table,
getspent
in
race:getspent
signifies that if
any of the functions
setspent
(),
getspent
(),
getspent_r
(), or
endspent
() are used in parallel in different threads of a program,
then data races could occur.
VERSIONS
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Many other systems provide a similar API.
STANDARDS
top
None.
SEE ALSO
top
getgrnam(3)
getpwnam(3)
getpwnam_r(3)
shadow(5)
COLOPHON
top
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Linux man-pages 6.16 2025-09-07
getspnam
(3)
Pages that refer to this page:
getent(1)
getpwnam(3)
setaliasent(3)
nsswitch.conf(5)
nscd(8)
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