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#include <pwd.h>
struct passwd *getpwnam(const char *name);
struct passwd *getpwnam_r(const char *name, struct passwd *pwd, char *buffer, int buflen);
struct passwd *getpwent(void);
struct passwd *getpwent_r(struct passwd *pwd, char *buffer, int buflen);
struct passwd *getpwuid(uid_t uid);
struct passwd *getpwuid_r(uid_t uid, struct passwd * pwd, char *buffer, int buflen);
void setpwent(void);
void endpwent(void);
struct passwd *fgetpwent(FILE *f);
struct passwd *fgetpwent_r(FILE *f, struct passwd *pwd, char *buffer, int buflen);
cc [ flag... ] file ... -D_POSIX_PTHREAD_SEMANTICS [ library... ]
int getpwnam_r(const char *name,struct passwd *pwd, char *buffer, size_t bufsize struct passwd **result);
int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer, size_t bufsize struct passwd **result);
See the subsection ‘Reentrant Interfaces’ in the DESCRIPTION section of this page.
These functions are used to obtain password entries. Entries can come from any of the sources for passwd specified in the /etc/nsswitch.conf file (see nsswitch.conf(4) ).
getpwnam() searches for a password entry with the login name specified by the character string parameter name.
getpwuid() searches for a password entry with the (numeric) user id specified by the parameter uid.
The functions setpwent(), getpwent(), and endpwent() are used to enumerate password entries from the database. setpwent() sets (or resets) the enumeration to the beginning of the set of password entries. This function should be called before the first call to getpwent(). Calls to getpwnam() and getpwuid() leave the enumeration position in an indeterminate state. Successive calls to getpwent() return either successive entries or NULL, indicating the end of the enumeration.
endpwent() may be called to indicate that the caller expects to do no further password retrieval operations; the system may then close the password file, deallocate resources it was using, and so forth. It is still allowed, but possibly less efficient, for the process to call more password functions after calling endpwent().
fgetpwent(), unlike the other functions above, does not use nsswitch.conf; it reads and parses the next line from the stream f, which is assumed to have the format of the passwd file. See passwd(4) .
The functions getpwnam(), getpwuid(), getpwent(), and fgetpwent() use static storage that is re-used in each call, making these routines unsafe for use in multithreaded applications.
The parallel functions getpwnam_r(), getpwuid_r(), getpwent_r(), and fgetpwent_r() provide reentrant interfaces for these operations.
Each reentrant interface performs the same operation as its non-reentrant counterpart, named by removing the ‘_r’ suffix. The reentrant interfaces, however, use buffers supplied by the caller to store returned results, and are safe for use in both single-threaded and multithreaded applications.
Each reentrant interface takes the same parameters as its non-reentrant counterpart, as well as the following additional parameters. The parameter pwd must be a pointer to a struct passwd structure allocated by the caller. On successful completion, the function returns the password entry in this structure. The parameter buffer is a pointer to a buffer supplied by the caller, used as storage space for the password data. All of the pointers within the returned struct passwd pwd point to data stored within this buffer; see RETURN VALUES. The buffer must be large enough to hold all the data associated with the password entry. The parameter buflen (or bufsize for the POSIX versions) should give the size in bytes of buffer. The POSIX versions place a pointer to the modified pwd structure in the result parameter, instead of returning a pointer to this structure.
For enumeration in multithreaded applications, the position within the enumeration is a process-wide property shared by all threads. setpwent() may be used in a multithreaded application but resets the enumeration position for all threads. If multiple threads interleave calls to getpwent_r(), the threads will enumerate disjoint subsets of the password database.
Like their non-reentrant counterparts, getpwnam_r() and getpwuid_r() leave the enumeration position in an indeterminate state.
Password entries are represented by the struct passwd structure defined in <pwd.h>:
struct passwd { char *pw_name; /* user’s login name */ char *pw_passwd; /* no longer used */ uid_t pw_uid; /* user’s uid */ gid_t pw_gid; /* user’s gid */ char *pw_age; /* not used */ char *pw_comment; /* not used */ char *pw_gecos; /* typically user’s full name */ char *pw_dir; /* user’s home dir */ char *pw_shell; /* user’s login shell */ };
The functions getpwnam(), getpwnam_r(), getpwuid(), and getpwuid_r() each return a pointer to a struct passwd if they successfully locate the requested entry; otherwise they return NULL . The POSIX functions getpwnam_r() and getpwuid_r() return zero upon success, or the error number in case of failure.
The functions getpwent(), getpwent_r(), fgetpwent(), and fgetpwent_r() each return a pointer to a struct passwd if they successfully enumerate an entry; otherwise they return NULL , indicating the end of the enumeration.
The functions getpwnam(), getpwuid(), getpwent(), and fgetpwent() use static storage, so returned data must be copied before a subsequent call to any of these functions if the data is to be saved.
When the pointer returned by the reentrant functions getpwnam_r(), getpwuid_r(), getpwent_r(), and fgetpwent_r() is non-NULL , it is always equal to the pwd pointer that was supplied by the caller.
The pw_passwd field in the passwd structure should not be used as the encrypted password for the user; use getspnam() or getspnam_r() instead. See getspnam(3C) .
Programs that use the interfaces described in this manual page cannot be linked statically since, the implementations of these functions employ dynamic loading and linking of shared objects at run time.
Use of the enumeration interfaces getpwent() and getpwent_r() is discouraged; enumeration is supported for the passwd file, NIS, and NIS +, but in general is not efficient and may not be supported for all database sources. The semantics of enumeration are discussed further in nsswitch.conf(4) .
Previous releases allowed the use of ‘+’ and ‘-’ entries in /etc/passwd to selectively include and exclude NIS entries. The primary usage of these ‘+/-’ entries is superseded by the name service switch, so the ‘+/-’ form may not be supported in future releases.
If required, the ‘+/-’ functionality can still be obtained for NIS by specifying compat as the source for passwd.
If the ‘+/-’ functionality is required in conjunction with NIS +, specify both compat as the source for passwd and nisplus as the source for the pseudo-database passwd_compat. See passwd(4) , shadow(4) , and nsswitch.conf(4) for details.
If the ‘+/-’ is used, both /etc/shadow and /etc/passwd should have the same ‘+’ and ‘-’ entries to ensure consistency between the password and shadow databases.
If a password entry from any of the sources contains an empty uid or gid field, that entry will be ignored by the files, NIS , and NIS+ name service switch backends. This will cause the user to appear unknown to the system.
If a password entry contains an empty gecos, home directory, or shell field, getpwnam() and getpwnam_r() return a pointer to a null string in the respective field of the passwd structure.
If the shell field is empty, login(1) automatically assigns the default shell. See login(1) .
Solaris 2.4 and earlier releases provided definitions of the getpwnam_r() and getpwuid_r() functions as specified in POSIX.1c Draft 6. The final POSIX.1c standard changed the interface for these functions. Support for the Draft 6 interface is provided for compatibility only and may not be supported in future releases. New applications and libraries should use the POSIX standard interface.
For POSIX.1c complaint applications, the _POSIX_PTHREAD_SEMANTICS and _REENTRANT flags are automatically turned on by defining the _POSIX_C_SOURCE flag with a value >= 199506L.