AIX Version 4.3 Differences Guide

6.5 Daylight Savings Time
Before AIX Version 4.3, daylight savings time could be selected through SMIT,
but the date of change for this characteristic was restricted to USA standard.
Once the daylight savings YES or NO question had been answered, a list of
available time zones was presented, but there was no option within SMIT for
specifying the start and end dates for daylight savings.
By default, the daylight saving time starts on the first Sunday of April at 2:00am
and stops on the last Sunday of October at 2:00am. AIX Version 4.3 now has the
capability of overriding these settings by specifying the start time and stop time in
the TZ environment variable.
Additional fields have been added to the SMIT time setting menu to set the TZ
variable. A back-end script performs the actual setting of the TZ variable.
6.6 Login Performance
The original design of the UNIX/AIX login system dates back to the early days of
UNIX when the number of users to be catered for was relatively small. As such,
the login process was perfectly adequate. With the commercial acceptance of
UNIX, however, the number of users per system has grown dramatically with tens
of thousands of users now being seen on some servers. This increase in the
number of users has highlighted some of the deficiencies in the original design of
the login process that are now beginning to affect system performance.
A problem exists, which once a user has entered their name and password, the
system must then search through the /etc/passwd and /etc/security/passwd files
trying to find a match for that user and, if successful, must also update a number
of other files. All the files are searched sequentially, and the time consumed can
be substantial if there are a large number of records to search through. In
extreme cases, if a user’s entry is near the end of the files, it is possible for the
login attempt to time out before completion. Also, the amount of CPU time being
consumed by the login process is a cause for concern. Login CPU usage has
been recorded as high as 47 percent on some systems.
The three major bottlenecks that have been identified are:
• Reading the /etc/passwd file
• Reading the /etc/security/passwd file
• Updating the /etc/security/lastlog file
A limited solution was used in previous versions of AIX to address some of these
issues by creating a hashed version of the /etc/passwd file. The mkpasswd
command took the /etc/passwd file as input and created the /etc/passwd.dir and
/etc/passwd.pag files. Then during login, if these hashed files existed, they were
read instead of the ASCII file. This partial solution provided some relief, but there
were still other areas that could also be improved.
A further improvement has been introduced in AIX Version 4.3 that provides
indexed access to the data files instead of sequential reads. Indexes are created
using the user name and user ID as keys with offsets into the data file. The data
118 AIX Version 4.3 Differences Guide