To improve login response time and conserve CPU time in systems with many users, AIX can use a hashed version of the /etc/passwd file to look up userids. When this facility is used, the /etc/passwd file still exists, but is not used in normal processing. The hashed versions of the file (/etc/passwd.dir and /etc/passwd.pag) are built by the mkpasswd command. If the hashed versions are not current, login processing reverts to a slow, CPU-intensive sequential search through /etc/passwd.
Once the hashed password files have been built, if the passwd, mkuser, chuser, rmuser commands (or the smit equivalents, with fast paths of the same name) are used to administer user IDs, the hashed files are kept up to date automatically. If the /etc/passwd file is changed with an editor or with the pwdadm command, the hashed files must be rebuilt with the command:
# mkpasswd /etc/passwd