System AdministrationBased on book chapter 141System AdministrationBecoming super-user user id (0)be aware....login as rootuse su utilityuse sudo2System AdministrationWhen you start a Linux system, the following sequence of events occurs:The hardware performs diagnostic self-tests.The Linux kernel is loaded from the /boot directory on the root device.The kernel starts running and initializes itself.The kernel starts init, the first user-mode process.3System AdministrationRun levels are defined in "/etc/inittab." The commonly predefined run levels are:0 halt1 single-user (i.e., maintenance)2 multi-user without networking3 server (full multi-user)5 workstation (full multi-user, graphical login)6 reboot4System AdministrationStopping LinuxUtility: shutdown -hkr time [ message ]shutdown time must be specified in one of three ways:now: the system is shut down immediately.+minutes: the system is shut down in the specified number of minutes.hours:minutes: the system is shut down at the specified time (24-hour format).The specified warning message (or a default one if none is specified) is displayed periodically as the time of shutdown approaches. Logins are disabled five minutes prior to shutdown.5System AdministrationUtility: shutdown -hkr time [ message ]If neither -h nor -k is specified, shutdown brings the system down to single-user mode by signaling init to change to run level 1. Using the -h option causes shutdown to change the run level to 0 (halt). The -r option causes shutdown to change the run level to 6 (reboot). The -k option is funny; it causes shutdown to behave as if were going to shut down the system, but when the shutdown time arrives, it does nothing. The "k" stands for "just kidding"!6File System IntegrityUtility: fsck -p [ fileSystem ]*fsck (file system check) scans the specified file systems and checks them for consistency. The kind of consistency errors that can exist include:A block is marked as free in the bitmap but is also referenced from an inode.A block is marked as used in the bitmap but is never referenced from an inode.More than one inode refers to the same block.An invalid block number.An inode's link count is incorrect.A used inode is not referenced from any directory.7Disk SpaceUtility: df [ fileSystem ]*df (disk free) displays a table of used and available disk space on the specified mounted file systems. If no file system is specified, all mounted file systems are described.8Disk SpaceUtility: du [-h] [-s] [ fileName ]*du displays the number of kilobytes that are allocated to each of the specified filenames. If a filename refers to a directory, its files are recursively described. When the -h option is used, the numeric values are changed to more human-readable values (i.e., 63844 blocks is displayed as 63M). When used with the -s option, du displays only the grand total (summary) for each file or directory. If no filenames are specified, the current directory is scanned.9System AdministrationCreating new file system1. Partition and format the drive if necessary 2. Create a file system on the medium.3. Mount the disk into the file system hierarchy.10System AdministrationUtility: mkfs -t type specialFile [ sectorCount ]mkfs creates a new file system on the specified special file. A new file system consists of a superblock, an inode list, a root directory, and a "lost+found" directory. The file system is built to be sectorCount sectors in size. Only a super-user can use this command.As with fsck, mkfs is really a front-end to a specific file system creator for each specific file system supported (e.g., mke2fs), determined by the file system type specified by type.11System AdministrationUser accountsAdd a new entry to the password file (and shadow password file if in use).what is this “shadow password business”?Add a new entry to the group file.Create a home directory for the user.Provide the user with some appropriate startup files.12System AdministrationUser accountsUtility: useradd [ -d directory ] [ -s shell ] userNameuseradd creates a new user on the system called userName. When -d is specified, make the new user's home directory. If -s is specified, make the new user's login shell. The next available UID is assigned to the new user.13System AdministrationUser accountsUtility: userdel [ -r ] userNameuserdel removes a user account from the system. If -r is specified, the user's home directory is removed as well.14System AdministrationPassword Filelocated in /etc/passwdformat:username:password:userId:groupId:personal:homedir:startup15System Administration16System AdministrationThe Group FileTo add a new user, you must decide which group the user will belong to and then search the group file to find the associated group ID. Every group in the system has an entry in the group file ("/etc/group") in the format:groupname:groupPassword:groupId:users17System Administration18System AdministrationInstalling new softwareUtility: rpm -aiqU packageNamerpm installs or updates an RPM package in the file packageName depending on whether -i or -U is specified. If the -q option is specified, the system is queried to see if packageName is currently installed. If -q is used with -a, all packages installed on the system are listed.19System AdministrationPeripheral devicesThe basic steps of device installation are as follows:1. Install the device driver if it isn't currently in the kernel and loadable device drivers are not used.2. Determine the device's major and minor numbers.3. Use mknod to associate a filename in "/dev" with the new device.20System AdministrationUtility: mknod fileName [ c] [ b ] majorNumber minorNumbermknod fileName pmknod creates the special file fileName in the file system. The first form of mknod allows a super-user to create either a character-oriented or block-oriented special file with the specified major and minor numbers. The major number identifies the class of the device, and the minor number identifies the instance of the device. The second form of mknod creates a named pipe, and may be used by anyone (or the mkfifo command may also be used).21Network InterfaceInformation about the network interface is given by the ifconfig commandifconfig can be used to manage network, e.g.ifconfig eth0 194.27.1.14