On Wed, Oct 13, 2010 at 17:16, Spiro Harvey <spiro at knossos.net.nz> wrote: > John Kennedy <skebi69 at gmail.com> wrote: > > This also does not tell me how useradd knows that on this system at > > this time the highest UID assigned to a user is 20015. > > From the source's mouth (this is from useradd.c in the shadow-utils > package): > > /* > * find_new_uid - find the next available UID > * > * find_new_uid() locates the next highest unused UID in the password > * file, or checks the given user ID against the existing ones for > * uniqueness. > */ > static void find_new_uid (void) > { > const struct passwd *pwd; > uid_t uid_min, uid_max; > > uid_min = getdef_unum ("UID_MIN", 1000); > uid_max = getdef_unum ("UID_MAX", 60000); > > /* > * Start with some UID value if the user didn't provide us with > * one already. > */ > if (!uflg) > user_id = uid_min; > > /* > * Search the entire password file, either looking for this > * UID (if the user specified one with -u) or looking for the > * largest unused value. > */ > #ifdef NO_GETPWENT > pw_rewind (); > while ((pwd = pw_next ())) { > #else /* using getpwent() we can check against > NIS users etc. */ > setpwent (); > while ((pwd = getpwent ())) { > #endif > if (strcmp (user_name, pwd->pw_name) == 0) { > fprintf (stderr, _("%s: name %s is not unique\n"), > Prog, user_name); > #ifdef WITH_AUDIT > audit_logger (AUDIT_USER_CHAUTHTOK, Prog, "adding > user", > user_name, user_id, 0); > #endif > exit (E_NAME_IN_USE); > } > if (uflg && user_id == pwd->pw_uid) { > fprintf (stderr, _("%s: UID %u is not unique\n"), > Prog, (unsigned int) user_id); > #ifdef WITH_AUDIT > audit_logger (AUDIT_USER_CHAUTHTOK, Prog, "adding > user", > user_name, user_id, 0); > #endif > exit (E_UID_IN_USE); > } > if (!uflg && pwd->pw_uid >= user_id) { > if (pwd->pw_uid > uid_max) > continue; > user_id = pwd->pw_uid + 1; > } > } > > /* > * If a user with UID equal to UID_MAX exists, the above algorithm > * will give us UID_MAX+1 even if not unique. Search for the first > * free UID starting with UID_MIN (it's O(n*n) but can be avoided > * by not having users with UID equal to UID_MAX). --marekm > */ > if (!uflg && user_id == uid_max + 1) { > for (user_id = uid_min; user_id < uid_max; user_id++) { > #ifdef NO_GETPWENT > pw_rewind (); > while ((pwd = pw_next ()) > && pwd->pw_uid != user_id); > if (!pwd) > break; > #else > if (!getpwuid (user_id)) > break; > #endif > } > if (user_id == uid_max) { > fprintf (stderr, _("%s: can't get unique UID\n"), > Prog); > fail_exit (E_UID_IN_USE); > } > } > } > > > > -- > Spiro Harvey Knossos Networks Ltd > 021-295-1923 www.knossos.net.nz > > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > > This looks like what I am talking about. Interesting to see that the program literally does what the code above does (as much as I can tell. I am not a coder) Thanks Spiro. John -- John Kennedy -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.centos.org/pipermail/centos/attachments/20101014/505fdc2e/attachment-0004.html>