System Administration in UNIX:Unix Administration Tasks and Starting and Shutting Down.

Module 19: System Administration in UNIX

In the context of the OS service provisioning, system administration plays a pivotal role. This is particularly the case when a system is accessed by multiple users. The primary task of a system administrator is to ensure that the following happens:

a. The top management is assured of efficiency in utilization of the system's resources.

b. The general user community gets the services which they are seeking.

In other words, system administrators ensure that there is very little to complain about the system's performance or service availability.

In Linux environment with single user PC usage, the user also doubles up as a system administrator. Much of what we discuss in Unix context applies to Linux as well.

In all Unix flavours there is a notion of a superuser privilege. Most major administrative tasks require that the system administrator operates in the superuser mode with root privileges. These tasks include starting up and shutting down a system, opening an account for a new user and giving him a proper working set-up. Administration tasks also involve installation of new software, distributing user disk space, taking regular back-ups, keeping system logs, ensuring secure operations and providing network services and web access.

We shall begin this module by enlisting the tasks in system administration and offering exposition on most of these tasks as the chapter develops.

19.1 Unix Administration Tasks

Most users are primarily interested in just running a set of basic applications for their professional needs. Often they cannot afford to keep track of new software releases and patches that get announced. Also, rarely they can install these themselves. In addition, these are non-trivial tasks and can only be done with superuser privileges.

Users share resources like disk space, etc. So there has to be some allocation policy of the disk space. A system administrator needs to implement such a policy. System administration also helps in setting up user's working environments.

On the other hand, the management is usually keen to ensure that the resources are used properly and efficiently. They seek to monitor the usage and keep an account of system usage. In fact, the system usage pattern is often analysed to help determine the efficacy of usage. Clearly, managements' main concerns include performance and utilisation of resources to ensure that operations of the organisation do not suffer.

At this juncture it may be worth our while to list major tasks which are performed by system administrators. We should note that most of the tasks require that the system administrator operates in superuser mode with root privileges.

19.1.1 Administration Tasks List

This is not an exhaustive list, yet it represents most of the tasks which system administrators perform:

1. System startup and shutdown: In the Section 19.2, we shall see the basic steps required to start and to stop operations in a Unix operational environment.

2. Opening and closing user accounts: In Unix an administrator is both a user and a super-user. Usually, an administrator has to switch to the super-user mode with root privileges to open or close user accounts. In Section 19.3, we shall discuss some of the nuances involved in this activity.

3. Helping users to set up their working environment: Unix allows any user to customize his working environment. This is usually achieved by using .rc files. Many users need help with an initial set-up of their .rc files. Later, a user may modify his .rc files to suit his requirements. In Section 19.4, we shall see most of the useful .rc files and the interpretations for various settings in these files.

4. Maintaining user services: Users require services for printing, mail Web access and chat. We shall deal with mail and chat in Section 19.4 where we discuss .rc files and with print services in Section 19.5 where we discuss device management and services. These services include spooling of print jobs, provisioning of print quota, etc.

5. Allocating disk space and re-allocating quotas when the needs grow: Usually there would be a default allocation. However, in some cases it may be imperative to enhance the allocation. We shall deal with the device oriented services and management issues in Section 19.5.

6. Installing and maintaining software: This may require installing software patches from time to time. Most OSs are released with some bugs still present. Often with usage these bugs are identified and patches released. Also, one may have some software installed which satisfies a few of the specialized needs of the user

community. As a convention this is installed in the directory /usr/local/bin. The local is an indicator of the local (and therefore a non-standard) nature of software. We shall not discuss the software installation as much of it is learned from experienced system administrators by assisting them in the task.

7. Installing new devices and upgrading the configuration: As a demand on a system grows, additional devices may need to be installed. The system administrator will have to edit configuration files to identify these devices. Some related issues shall be covered in section 19.5 later in this chapter.

8. Provisioning the mail and internet services: Users connected to any host shall seek Mail and internet Web access. In addition, almost every machine shall be a resource within a local area network. So for resource too the machine shall have an IP address. In most cases it would be accessible from other machine as well. We shall show the use .mailrc files in this context later in Section 19.4.

9. Ensuring security of the system: The internet makes the task of system administration both interesting and challenging. The administrators need to keep a check on spoofing and misuse. We have discussed security in some detail in the module on OS and Security.

10. Maintaining system logs and profiling the users: A system administrator is required to often determine the usage of resources. This is achieved by analysing system logs. The system logs also help to profile the users. In fact, user profiling helps in identifying security breaches as was explained in the module entitled OS and Security.

11. System accounting: This is usually of interest to the management. Also, it helps system administrators to tune up an operating system to meet the user requirements. This also involves maintaining and analysing logs of the system operation.

12. Reconfiguring the kernel whenever required: Sometimes when new patches are installed or a new release of the OS is received, then it is imperative to compile the kernel. Linux users often need to do this as new releases and extensions become available.

Let us begin our discussions with the initiation of the operations and shutdown procedures.

19.2 Starting and Shutting Down

First we shall examine what exactly happens when the system is powered on. Later, we shall examine the shutdown procedure for Unix systems. Unix systems, on being powered on, usually require that a choice be made to operate either in single or in multiple-user mode. Most systems operate in multi-user mode. However, system administrators use single-user mode when they have some serious reconfiguration or installation task to perform. Family of Unix systems emanating from System V usually operate with a run level. The single-user mode is identified with run level s, otherwise there are levels from 0 to 6. The run level 3 is the most common for multi-user mode of operation.

On being powered on, Unix usually initiates the following sequence of tasks:

1. The Unix performs a sequence of self-tests to determine if there are any hardware problems.

2. The Unix kernel gets loaded from a root device.

3. The kernel runs and initializes itself.

4. The kernel starts the init process. All subsequent processes are spawned from init process.

5. The init checks out the file system using fsck.

6. The init process executes a system boot script.

7. The init process spawns a process to check all the terminals from which the system may be accessed. This is done by checking the terminals defined under

/etc/ttytab or a corresponding file. For each terminal a getty process is launched. This reconciles communication characteristics like baud rate and type for each terminal.

8. The getty process initiates a login process to enable a prospective login from a terminal.

During the startup we notice that fsck checks out the integrity of the file system. In case the fsck throws up messages of some problems, the system administrator has to work around to ensure that there is a working configuration made available to the users. It will suffice here to mention that one may monitor disk usage and reconcile the disk integrity. The starting up of systems is a routine activity. The most important thing to note is that on booting, or following a startup, all the temporary files under tmp directory are cleaned

up. Also, zombies are cleaned up. System administrators resort to booting when there are a number of zombies and often a considerable disk space is blocked in the tmp directory. We next examine the shutdown. Most Unix systems require invoking the shutdown utility. The shutdown utility offers options to either halt immediately, or shutdown after a pre-assigned period. Usually system administrators choose to shutdown with a pre- assigned period. Such a shutdown results in sending a message to all the terminals that the system shall be going down after a certain interval of time, say 5 minutes. This cautions all the users and gives them enough time to close their files and terminate their active processes. Yet another shutdown option is to reboot with obvious implications. The most commonly used shutdown command is as follows:

shutdown -h time [message]

Here the time is the period and message is optional, but often it is intended to advise users to take precautions to terminate their activity gracefully. This mode also prepares to turn power off after a proper shutdown. There are other options like k, r, n etc. The readers are encouraged to find details about these in Unix man pages. For now, we shall move on to discuss the user accounts management and run command files.