getspnam, getspnam_r, getspent, getspent_r, setspent, endspent, fgetspent,
fgetspent_r, sgetspent, sgetspent_r, putspent, lckpwdf, ulckpwdf - get shadow
password file entry
Standard C library (
libc,
-lc)
/* General shadow password file API */
#include <shadow.h>
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 *s);
int putspent(const struct spwd *p, FILE *stream);
int lckpwdf(void);
int ulckpwdf(void);
/* GNU extension */
#include <shadow.h>
int getspent_r(struct spwd *spbuf,
char buf[.buflen], size_t buflen, struct spwd **spbufp);
int getspnam_r(const char *name, struct spwd *spbuf,
char buf[.buflen], size_t buflen, struct spwd **spbufp);
int fgetspent_r(FILE *stream, struct spwd *spbuf,
char buf[.buflen], size_t buflen, struct spwd **spbufp);
int sgetspent_r(const char *s, struct spwd *spbuf,
char buf[.buflen], size_t buflen, struct spwd **spbufp);
getspent_r(),
getspnam_r(),
fgetspent_r(),
sgetspent_r():
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
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
s 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.
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
buflen. 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.
The shadow password structure is defined in
<shadow.h> 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 */
};
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.
- EACCES
- The caller does not have permission to access the shadow
password file.
- ERANGE
- Supplied buffer is too small.
- /etc/shadow
- local shadow password database file
- /etc/.pwd.lock
- lock file
The include file
<paths.h> defines the constant
_PATH_SHADOW
to the pathname of the shadow password file.
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 (), endspent (), getspent_r () |
Thread safety |
MT-Unsafe race:getspent locale |
fgetspent () |
Thread safety |
MT-Unsafe race:fgetspent |
sgetspent () |
Thread safety |
MT-Unsafe race:sgetspent |
putspent (), getspnam_r (), sgetspent_r () |
Thread safety |
MT-Safe locale |
lckpwdf (), ulckpwdf (), fgetspent_r () |
Thread safety |
MT-Safe |
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.
The shadow password database and its associated API are not specified in
POSIX.1. However, many other systems provide a similar API.
getgrnam(3),
getpwnam(3),
getpwnam_r(3),
shadow(5)