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#include <grp.h>
struct group { char *gr_name; /* group name */ char *gr_passwd; /* group password */ gid_t gr_gid; /* group id */ char **gr_mem; /* group members */ };
The functions getgrnam() and getgrgid() search the group database for the given group name pointed to by name or the group id pointed to by gid, respectively, returning the first one encountered. Identical group names or group gids may result in undefined behavior.
The getgrent() function sequentially reads the group database and is intended for programs that wish to step through the complete list of groups.
The functions getgrent_r(), getgrnam_r(), and getgrgid_r() are thread-safe versions of getgrent(), getgrnam(), and getgrgid(), respectively. The caller must provide storage for the results of the search in the grp, buffer, bufsize, and result arguments. When these functions are successful, the grp argument will be filled-in, and a pointer to that argument will be stored in result. If an entry is not found or an error occurs, result will be set to NULL.
These functions will open the group file for reading, if necessary.
The setgroupent() function opens the file, or rewinds it if it is already open. If stayopen is non-zero, file descriptors are left open, significantly speeding functions subsequent calls. This functionality is unnecessary for getgrent() as it does not close its file descriptors by default. It should also be noted that it is dangerous for long-running programs to use this functionality as the group file may be updated.
The setgrent() function is identical to setgroupent() with an argument of zero.
The endgrent() function closes any open files.
The function setgroupent() returns the value 1 if successful, otherwise the value 0 is returned. The functions endgrent(), setgrent() and setgrfile() have no return value.
/etc/group | |
group database file | |
The functions getgrent(), getgrent_r(), endgrent(), setgroupent(), and setgrent() are fairly useless in a networked environment and should be avoided, if possible. The getgrent() and getgrent_r() functions make no attempt to suppress duplicate information if multiple sources are specified in nsswitch.conf(5).
GETGRENT (3) | July 31, 2016 |
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