The Group Files and Routines

• Groups are very weak in linux.
  • They should allow for shared file access.
  • But in general this does not work due to human problems.
• /etc/group
  • Group name.
  • Encrypted passwd, same as /etc/passwd
  • Group ID
  • List of users in the group.
• /etc/gshadow
  • The group name.
  • The encrypted password
  • A list of administrators, or members of the group that are allowed to change the password or members of the group.
  • a list of members.
• Some system commands
  • gpasswd: change the group password for a given group
  • grpck: checks to see if the group files are consistent and valid
  • newgrp: changes the group the user is currently using
• Routines
  • Very much like passwd

    #include <sys/types.h>
    #include <grp.h>
    struct group *getgrnam(const char *name);
    struct group *getgrgid(gid_t gid);
    struct group *getgrent(void);
    void setgrent(void);
    void endgrent(void);
    struct group *fgetgrent(FILE *stream);
    
    struct group {
        char   *gr_name;        /* group name */
        char   *gr_passwd;      /* group password */
        gid_t   gr_gid;         /* group ID */
        char  **gr_mem;         /* NULL-terminated array of pointers
                                   to names of group members */
    };