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SYNOPSIS top

/* 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(size_t size;struct spwd *spbuf,charbuf[size], size_tsize, struct spwd **spbufp);int getspnam_r(size_t size;const char *name, struct spwd *spbuf,charbuf[size], size_tsize, struct spwd **spbufp);int fgetspent_r(size_t size;FILE *stream, struct spwd *spbuf,charbuf[size], size_tsize, struct spwd **spbufp);int sgetspent_r(size_t size;const char *s, struct spwd *spbuf,charbuf[size], size_tsize, struct spwd **spbufp); Feature Test Macro Requirements for glibc (seefeature_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 top

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., seegetpwnam(3) andgetpwent(3)). Thegetspnam() function returns a pointer to a structure containing the broken-out fields of the record in the shadow password database that matches the usernamename. Thegetspent() function returns a pointer to the next entry in the shadow password database. The position in the input stream is initialized bysetspent(). When done reading, the program may callendspent() so that resources can be deallocated. Thefgetspent() function is similar togetspent() but uses the supplied stream instead of the one implicitly opened bysetspent(). Thesgetspent() function parses the supplied strings into a structspwd. Theputspent() function writes the contents of the supplied structspwd *p as a text line in the shadow password file format tostream. String entries with value NULL and numerical entries with value -1 are written as an empty string. Thelckpwdf() 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). Theulckpwdf() function releases the lock again. Note that there is no protection against direct access of the shadow password file. Only programs that uselckpwdf() 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. Thegetspnam_r() function is likegetspnam() but stores the retrieved shadow password structure in the space pointed to byspbuf. This shadow password structure contains pointers to strings, and these strings are stored in the bufferbuf of sizesize. 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 functionsgetspent_r(),fgetspent_r(), andsgetspent_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 */ };

RETURN VALUE top

The functions that return a pointer return NULL if no more entries are available or if an error occurs during processing. The functions which haveint as the return value return 0 for success and -1 for failure, witherrno 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.

/etc/shadow local shadow password database file/etc/.pwd.lock lock file The include file<paths.h> defines the constant_PATH_SHADOWto the pathname of the shadow password file.

ATTRIBUTES top

For an explanation of the terms used in this section, seeattributes(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 inrace:getspent signifies that if any of the functionssetspent(),getspent(),getspent_r(), orendspent() are used in parallel in different threads of a program, then data races could occur.

COLOPHON top

This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-06-28getspnam(3)

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