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 -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 197 bytes Desc: not available URL: <http://lists.centos.org/pipermail/centos/attachments/20101014/387df904/attachment-0004.sig>