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GETSPNAM(3) Linux Programmer's Manual GETSPNAM(3)
getspnam, getspnam_r, getspent, getspent_r, setspent, endspent, fget‐
spent, fgetspent_r, sgetspent, sgetspent_r, putspent, lckpwdf, ulckp‐
wdf - get shadow password file entry
/* 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, size_t buflen, struct spwd **spbufp);
int getspnam_r(const char *name, struct spwd *spbuf,
char *buf, size_t buflen, struct spwd **spbufp);
int fgetspent_r(FILE *stream, struct spwd *spbuf,
char *buf, size_t buflen, struct spwd **spbufp);
int sgetspent_r(const char *s, struct spwd *spbuf,
char *buf, size_t buflen, 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
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.
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 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.
Structure
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 cause of 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(), │ 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.
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)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2016-03-15 GETSPNAM(3)
Pages that refer to this page: getent(1), getpwnam(3), setaliasent(3), nsswitch.conf(5), nscd(8)