unit 10

• System administration deals with all the things you have to do to keep your computer system in a stable and usable order.
• System administration can include tasks such as backing up files, installing new programs, managing accounts, and keeping the integrity of the file system.
• Understanding the organisation of the file system tree can make your job as a sys admin easier.
• This understanding comes through experience.
• There are many different directories and files with varying importance in the file system tree.
• This unit will focus on two main areas: /var and /etc.
• /var contains spool directories, log files, accounting information and various other items.
• Sub-directories of /var include /var/adm, which holds logs and setup records, /var/log, which holds various system log files, /var/spool, which holds spooling directories for printers, mail, etc., and /var/tmp, which holds temporary space.
• System daemons, the kernel, utilities and services all produce data that is logged, which is stored in various 'log files'.
• Log files can be very useful in determining any issues with the system.
• For example, if a daemon refuses to start, check the log files.
• The log files have a limited useful life span and there should be a clear retention policy.
• Most log files are text files and can be easily viewed with standard tools such as cat, more, grep.
• UNIX can be inconsistent with the location of log files, but Linux is better.
• Having a clear logging and retention policy is very important.
• Different distributions of Linux have their own ways of naming and dividing up log files, but generally, Linux sends log files to the /var/log directory.
• The /var directory is specific for each computer or server.
• dmesg is used to examine or control the kernel ring buffer and can assist in determining any errors or problems with the system.
• httpd is a web server daemon and the Apache HyperText Transfer Protocol (HTTP) server program, it runs as a standalone daemon process.
• Mysqld.log logs each SQL statement received from clients.
• Examples of services that run at start-up include httpd, init.d, mysqld, ntpd, and ftpd.
• The ‘syslog’ file can be viewed using ‘more’ and is a record of system activity.
• These initialise during the boot process of your system.
• The purpose of the ‘syslog’ file is to record system activity.
• /etc/passwd consists of information about the user, including Username, Real name, Home directory, and other information about the user.
• For example, specifying Mail.info in /etc/syslog.conf results in mail messages being saved in /var/log/maillog.
• /etc/ is part of the root filesystem and is used for critical system and configuration files.
• Sudo has been largely superseded by ‘sudo’, which works in a similar way to ‘su’ but is more restricted in that it does not automatically grant full root privileges.
• Three services which are configured to run at start-up are httpd, init.d, and mysqld.
• /etc/init.d contains a number of start-up and stop scripts for various services on your system.
• Mysqld.log, also known as the MySQL Server, manages access to MySQL database and tables.
• Upon using the ‘sudo’ command, sudo consults the /etc/sudoers file to see if the user is authorised to use sudo.
• Upon typing ‘su’, you will be asked for a password, which can be the root password or the password of the user (su – username).
• Sudo is faster to use than use su or log in as root.
• Sudo keeps a log for the commands which were executed.
• At times, you may need to view sensitive files, such as those in /etc/passwd and /etc/shadow, and for this, you will need to use ‘su’ or ‘sudo’.
• The server writes information to this log when clients connect or disconnect.
• The other two service files are /etc/passwd and /etc/shadow.
• Some important files and directories in /etc are /etc/syslog.conf, /etc/init.d, /etc/passwd, and /etc/shadow.
• /etc/syslog.conf controls syslogd’s behaviour.