Major differences between 4.3 BSD and AIX

The following is a summary of the major differences between AIX® and 4.3 BSD systems.

On AIX, the network daemons are started from the /etc/rc.tcpip file, not the /etc/rc.local file. The /etc/rc.tcpip shell script is invoked from the /etc/inittab file, not the /etc/rc file.

If the System Resource Controller (SRC) is running, the TCP/IP daemons run under SRC control. If you do not want the TCP/IP daemons running under SRC control, use the smit setbootup_option fast path to change the system to BSD-style rc configuration.

These network management functions available on 4.3 BSD are supported by AIX:

• Kernel-level SYSLOG logging facilities
• Access rights for UNIX domain sockets.

Configuration data storage

4.3 BSD usually stores configuration data in ASCII files. Related pieces of information are kept on the same line and record processing (sorting and searching) can be done on the ASCII file itself. Records can vary in length and are terminated by a line feed. 4.3 BSD provides tools to convert some potentially large ASCII files to a database (dbm) format. Relevant library functions search the pair of dbm files if they exist, but search the original ASCII file if the dbm files are not found.

Some configuration data for AIX is stored in ASCII files, but often in a stanza format. A stanza is a set of related pieces of information stored in a group of several lines. Each piece of information has a label to make the contents of the file more understandable.

AIX also supports dbm versions of password and user information. Furthermore, the /etc/passwd, /etc/group, and /etc/inittab files are examples of files for AIX where the information is stored in traditional form rather than in stanza form.

Other configuration data for AIX are stored in files maintained by the Object Data Manager (ODM). System Management Interface Tool (SMIT) can manipulate and display information in ODM files. Alternatively, you can use the ODM commands directly to view these files. To query the ODM files, use the following commands:

• odmget
• odmshow.

The following ODM commands alter ODM files:

• odmadd
• odmcreate
• odmdrop
• odmchange
• odmdelete.

Attention: Altering ODM files incorrectly can cause the system to fail, and might prevent you from successfully restarting the system. Only use ODM commands directly on ODM files when task-specific commands, such as those generated by SMIT, is unsuccessful.

Configuration management

When a system running AIX starts up, a set of configuration-specific commands are invoked by the Configuration Manager. These configuration-specific commands are called methods. Methods identify the devices on the system and update the appropriate ODM files in the /etc/objrepos directory.

Device special files in the /dev directly are not preinstalled. Some special files, such as those for hard disks, are created automatically during the startup configuration process. Other special files, such as those for ASCII terminals, must be created by the system administrator by using the SMIT Devices menu. This information is retained in the ODM for later use by the system.

Disk management

In AIX, disk drives are referred to as physical volumes. Partitions are referred to as logical volumes. As in 4.3 BSD, a single physical volume can have multiple logical volumes. However, unlike 4.3 BSD, a single logical volume in AIX can span multiple physical volumes. To do this, you must make several physical volumes into a volume group and create logical volumes on the volume group.

Commands in AIX used for file system and volume management include:

• crfs
• varyonvg
• varyoffvg
• lsvg
• importvg
• exportvg.

The following 4.3 BSD commands are also available:

• mkfs
• fsck
• fsdb
• mount
• umount.

Differences between these commands for 4.3 BSD and for AIX are discussed in File systems for BSD 4.3 system managers.

4.3 BSD maintains a list of file systems in the /etc/fstab file. AIX maintains a stanza for each file system in the /etc/filesystems file.

The tn3270 command

The tn3270 command is a link to the telnet command, but it uses the /etc/map3270 file and the current TERM environment variable value to provide 3270 keyboard mappings. Thus, the tn3270 command operates exactly like the BSD version.

If you want to change the escape sequences from the defaults used by the tn3270, telnet, or tn commands, set the TNESC environment variable before starting these commands.

New commands

To handle new configuration and disk management systems, AIX has about 150 commands that are new to 4.3 BSD administrators.

Startup

AIX supports automatic identification and configuration of devices. Consequently, the startup process is very different from 4.3 BSD systems. In addition to the kernel, an image of a boot file system and the previous base device configuration information is loaded to a RAM disk. In the first phase of startup, sufficient configuration information is loaded and checked to permit accessing logical volumes. The paging space device is identified to the kernel and the hard disk root file system is checked. At this time, the operating system changes the root file system from the RAM disk to the hard disk and completes the startup procedure, including configuring other devices.

User authorization

4.3 BSD, and versions of AT&T UNIX operating systems before SVR4, store all user authentication information, including encrypted passwords, in the /etc/passwd file. Traditionally, the /etc/passwd file could be read by all.

On SVR4 systems, encrypted passwords are removed from the /etc/passwd file and stored in the /etc/shadow file. Only users with root authority and trusted programs (such as the /bin/login program) can read the /etc/shadow file.

AIX stores encrypted passwords in the /etc/security/passwd file. Other files in the /etc/security directory are the user and limits files. These three files define the way a user is allowed to access the system (such as using the rlogin or telnet commands) and the user's resource limits (such as file size and address space).

Printing

Most 4.3 BSD printing commands are supported with minor differences. One difference is that the /etc/qconfig file is the configuration file in AIX.

The line printing system for AIX can interoperate with the 4.3 BSD line printing system, both for submitting print jobs to 4.3 BSD systems and for printing jobs submitted from a 4.3 BSD system.

Shells

AIX supports the Bourne shell, C shell and Korn shell. The full path name for the Bourne shell program is /bin/bsh. The /bin/sh file is a hard link to the /bin/ksh file. This file can be changed by the administrator.

AIX does not support setuid or setgid for shell scripts in any shell.

Note:

1. AIX has no shell scripts that rely on the /bin/sh. However, many shell scripts from other systems rely on /bin/sh being the Bourne shell.
2. Although the Bourne shell and Korn shell are similar, the Korn shell is not a perfect superset of the Bourne shell.