Week Eleven Agenda

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Week Eleven Agenda. Announcements Open Source Presentation dates December 3and 10. Lab Assignment 11-1 Knoppix File System No script logic Link of the week Review week ten lab assignment Week ten expected outcomes Next lab assignment Break-out problems Upcoming deadlines
Week Eleven Agenda
  • Announcements
  • Open Source Presentation dates
  • December 3and 10.
  • Lab Assignment 11-1 Knoppix File System No script logic
  • Link of the week
  • Review week ten lab assignment
  • Week ten expected outcomes
  • Next lab assignment
  • Break-out problems
  • Upcoming deadlines
  • Lab assistance
  • Link of the weekFile System  Search for the web site written by M. Tim Jones (mti@mtjones.com) Anatomy of the Linux file system The syntax used at this web site will be useful when completing Lab Assignment 11-1. These are “under the hood” commands used by Graphical User Interfaces (GUI).Link of the weekWhat is a UNIX-like File system?A UNIX file system is a collection of files and directories stored on hard disk.  Each file system is stored in a separate whole disk partition. The following are some file systems: / - root file system contains files under several directories including /sbin, /tmp, /var, and /devWhat is in a file system? User data - information contained in files Metadata – information on the file system structure such as inodes, directories, and superblockLink of the weekIn general, every directory under the root directory is on the root partition, unless it has a separate entry in the full listing from df (or df -h with no other options).Every partition has its own file system. By imagining all those file systems together, we can form an idea of the tree-structure of the entire system. In a file system, a file is represented by an inode, a kind of serial number containing information about the actual data that makes up the file: to whom this file belongs, and where is it located on the hard disk.Link of the weekEvery partition has its own set of inodes; throughout a system with multiple partitions, files with the same inode number can exist.Why partition? One of the goals of having different partitions is to achieve higher data security in case of disaster. By dividing the hard disk in partitions, data can be grouped and separated. When an accident occurs, only the data in the partition that took the hit will be damaged, while the data on the other partitions will most likely remain intact. Link of the weekLinux File system ext3 includes journaling capabilities that allows for faster recovery after unexpected reboots. Journaling reduces the amount of time spent recovering a file system after a crash, and is therefore in high demand in environments where high availability is important, not only to improve recovery times on single machines but also to allow a crashed machine's file system to be recovered on another machine when we have a cluster of nodes with a shared disk.Link of the weekDefine file system with journaling : A file system with journaling is based on the techniques used from real-time transaction processing. A transaction log is used to store transactions either in a designated file system location or on a separate disk partition. As changes are made to the file system, metadata changes are recorded in the log and writing entries in the log are done prior to writing the actual buffers to disk.Link of the weekLinux file system with journaling In the event of a system crash, the entries in the log file remain intact and are replayed. Maintaining this level of data integrity ensures that the file system is in a constant state.Review week ten lab assignmentDefinition: Network Protocol is a standard procedure and format that two data communication devices must understand, accept and use in order to be able to communicate with each other. A network protocol determines the following: 1. The type of error checking to be performed. 2. The data compression method to be used. 3. How the sending device will indicate that it has finished sending a message. 4. How the receiving device will indicate that it has received a message.Review week ten lab assignment/etc/password file Location: /etc/passwd Field separators: Colon (:) File format: Username:Password:UID:GID:UserID:Home directory:Command/shellExample: dandrear:x:1020:1021:dandrear user:/home/dandrear:/bin/kshPermissions on Einstein: -rw-r--r-- 1 root root 1636 Aug 16 10:37 /etc/passwdReview week ten lab assignment/etc/passwd file
  • Username: It is used when user logs in. It should be between 1 and 32 characters in length.
  • Password: An x character indicates that encrypted password is stored in /etc/shadow file.
  • User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.
  • Group ID (GID): The primary group ID (stored in /etc/group file)
  • User ID Info: The comment field. It allow you to add extra information about the users such as user’s full name, phone number etc. This field use by finger command.
  • Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /
  • Command/shell: The absolute path of a command or shell (/bin/bash). Typically, this is a shell. Please not it does not have to be a shell.
  • Review week ten lab assignmentExample of /etc/passwd file root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin sync:x:5:0:sync:/sbin:/bin/sync shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown halt:x:7:0:halt:/sbin:/sbin/haltReview week ten lab assignment/etc/passwd file The /etc/passwd file is considered the user database for the system. The information contained in the /etc/passwd file is useful for applications running on the system to access. In summary, the /etc/passwd file is located under the system configuration and executables directory. The /etc/passwd file is the system’s master list of information about user accounts.Review week ten lab assignment/etc/shadow file Location: /etc/shadow Field separators: Colon (:) File format: username:passwd:lastpasswdch:min:max:warn:inactive:expire:unusedExample: dandrear:$1$dhBysgdhfteM9gd00:13064:0:99999:7:::Permissions on Einstein: -r-------- 1 root root 1107 Sep 5 15:24 /etc/shadow (Permission denied)Review week ten lab assignment/etc/shadow file
  • User name : It is your login name
  • Password: It your encrypted password. The password should be minimum 6-8 characters long including special characters/digits
  • Last password change (last changed): Days since Jan 1, 1970 that password was last changed
  • Minimum: The minimum number of days required between password changes i.e. the number of days left before the user is allowed to change his/her password
  • Maximum: The maximum number of days the password is valid (after that user is forced to change his/her password)
  • Warn : The number of days before password is to expire that user is warned that his/her password must be changed
  • Inactive : The number of days after password expires that account is disabled
  • Expire : days since Jan 1, 1970 that account is disabled i.e. an absolute date specifying when the login may no longer be used
  • Unused field:
  • Review week ten lab assignment/etc/shadow file
  • The “X” in the /etc/passwd file password field indicates that the shadow file contains the encrypted password.
  • Red Hat Linux uses MD5 by default.
  • Most Linux systems utilize MD5 as their encrypted form.
  • MD5 requires 34 characters in encryption form.
  • MD5 begins with a dollar sign, number, and a dollar sign (e.g. $1$ or $6$ …).
  • The shadow file is only readable by root.
  • In summary, the /etc/shadow file contains the encoded passwords and password settings. The /etc/shadow file contains all the guide lines that pertain to the administration of the password. Review week ten lab assignment/etc/group file Location: /etc/group Field separators: Colon (:) File format: Group name:Password:GID:User_listExample: faculty:x:410: staff:x:430:Permissions on Einstein: -rw-r--r-- 1 root root 833 Aug 16 10:37 groupReview week ten lab assignment/etc/group file
  • Group name: Name of the group.
  • Password: The group password is encrypted. If this field is empty, no password is needed. Otherwise, an “X” in the field indicates the password is stored in the /etc/gshadow file.
  • GID: The numerical group ID and/or unique group identifier.
  • User_list: All the group member's user names, separated by commas.
  • Most Unix-like systems impose a limit of 16 to 32 group memberships per user.Review week ten lab assignment/etc/group filentp:x:38: student:x:101: itadmin:x:400: faculty:x:410: csfac:x:420:mccannp,sieberth,hochstew,whittakt,morganr,hartung staff:x:430: hpsmh:x:501: kumarp:x:503: caldwelr:x:505: apache:x:48: oinstall:x:600:Linux utilizes the vigr command used to edit the /etc/group file.Review week ten lab assignment/etc/group fileIn summary, the /etc/group file identifies a collection of users who generally share similar functions. These groupings are not limited to departments or project.Review week ten lab assignment/etc/gshadow file
  • Group-name: is the name of the group
  • Password: is the encoded version of the password
  • Group-admins: is the list of members in the group
  • Additional- users: a copy of additional members.
  • In summary, the /etc/gshadow file is utilized to store the /etc/group password.Review week ten lab assignmentFile Summary /etc/passwd - user account information /etc/shadow - secure user password information /etc/group - group information /etc/gshadow - secure group password informationUser account files The /etc/passwd, /etc/shadow, and /etc/group files are considered the most important files for storing user account and authentication information.Command to add a user account Linux/Knoppix –useraddCommand to remove a user accountKnoppix – deluser Linux - userdelReview week ten lab assignmentManaging Users Adding a user to a computer involves several steps before the user can actually log in and perform user operations. Every user that intends to utilize a computer must first gain access to that system, then go through an initialization process found under the user’s home directory. The new user initialization process begins by reading and executing the commands and environmental variables found in the $HOME/.profile file or .bash_profile. Normally, the .profile is run automatically when you log into the system and the user’s environment is set up silently. Once the user is granted access permission to the system, a shell is spawn to allow the user to interact with the system. Review week ten lab assignmentManaging Users Display the ~dandrear/.profile When adding a new user account to the system, the administrator assigns the username a user identification number (UID). The UID is used internally by the system to identify each user. Duplicating the UID causes the accounts to share an identity in the system.Review week ten lab assignmentProcesses The & symbol represents the background process. Once a background process is launched by a terminal session, the process becomes unattached to the terminal that launched it. Background processes are terminated typing kill -9 <pid> Example: simple_script & Once a foreground process is started, it remains in the foreground until it completes, because it remains attached to the terminal. Foreground process by typing Ctl-CReview week ten lab assignmentKernel functions in two ways A responsive function is one where resource allocation and process creation and management, are initiated by requests from processes. An autonomous function is the allocation of memory and CPU, which are performed without explicitly requested by a user process. Daemon processes are started as part of the boot process and run until the system is shut down. Daemon processes can be associated with a systems database applications, network , secure terminal and file transfer, and scheduling tasksReview week ten lab assignmentUNIX inetd Daemon The UNIX inetd daemon may start the telnetd to handle a telnet connection. Inetd daemon may start the ftpd to handle an ftp connection. One daemon may start another; the UNIX inetddaemonwill accept a network connection and then start another daemon to handle the connection, based on the type of connection. There are various processes in UNIX that are not owned by a user, but exist to provide services. These processes are often called "daemons.“ The inetd superserver runs continuously listening for network connections. This type of daemon is more susceptible to be system breaches.Review week ten lab assignmentLinux xinetd daemon The Linus xinetd daemon is a more secure replacement for the inetd superserver. The xinetd superserver listens for network connections. When a connection is made, it launches a specific daemon and forwards the data from the socket to the daemon’s standard input. Basically, the xinetd superserver works on-demand.Review week ten lab assignmentSingle and Multi-Threaded Processes The implementation of a thread may differ from one operating system to another. Generally, a thread exists within a process. Multiple threads within a single process can co-exist and share the same resources. Review week ten lab assignmentThreads compared to Processes Threads exist as subsets of a process. Multiple threads in a single process share memory and other resources. Threads share the same address space. Threads utilize context switching the same as a process.Review week ten lab assignmentSingle and Multi-Threaded ProcessesSingle threaded process is when a process only performs one task. An embedded system is an example of a single threaded process (BIOS). Multiple threaded process is when a process can perform multiple tasks concurrently without extra overhead needed to create a new process. Word processor is a multiple threaded process.Review week ten lab assignmentKernel Functions The kernel is part of the operating system that allocates machine resources, including memory, disk space, and CPU cycles, to all other programs that run on a computer. The kernel can be responsible for creating the init process. The init process is created through a process called hand-crafted or spontaneous.Review week ten lab assignmentfork command Is a command that causes the shell to fork a new process, creating a duplicate of the shell process (sub-shell). execcommand The new process attempts to exec the command. If the command is a binary executable program, like a compiled C program, exec succeeds and the system overlays the newly created sub-shell with the executable program. The fork and exec commands are system calls that are executed by the operating system.Review week ten lab assignmentLinux Process StatesProcesses go through various process states during their existence. These are transitory states managed by the operating system (OS). The specifics of these process states vary from one OS to another, as well as state names.Waiting (process scheduler - load from secondary storage to main memory)Executing (after a process is assigned a processor by a short – term scheduler, context switch is performed)Stopped (The process has been stopped, usually by receiving a signal. A process that is being debugged can be in a stopped state or another task is executing )Zombie (This is a halted process for some reason. Still has a task_struct data structure)Review week ten lab assignmentReview week ten lab assignmentReview week ten lab assignmentA zombie process is one that has completed execution but still has an entry in the process table, allowing the process that started it to read its exit status. Remember that a zombie is already dead.Processes marked <defunct> are dead processes (so-called "zombies")Locate a zombie process on cs.franklin.edu Commands: ps -aux ps -aux | awk ‘{ print $8 “ “ $2 } ‘ Review week ten lab assignmentOrphan process is a process whose parent process has terminated or finished.Characteristics of an orphan process: The owner of an orphan process can kill that process. Logging off your terminal will not guarantee termination of your orphan. An orphan process may continue to execute, taking up system resources and slowing the machine down for other users. If you notice slow performance on a machine and you see an orphan process that doesn’t belong to you.Review week ten lab assignmentIs there an orphan process listed below?root 1 0 0 2010 ? 00:03:17 initdandrear 22387 22385 0 17:34 pts/1 00:00:00 grep initroot 927 1 0 2010 ? 00:08:58 /usr/sbin/sshdroot 22350 927 0 17:31 ? 00:00:00 sshd: dandrear@pts/1dandrear 22390 22385 0 17:34 pts/1 00:00:00 sort -rdandrear 22389 22385 0 17:34 pts/1 00:00:00 grep dandreardandrear 22388 22385 0 17:34 pts/1 00:00:00 ps -efdandrear 22385 22351 0 17:34 pts/1 00:00:00 /bin/ksh ./pid_ppid.sh dandreardandrear 22351 22350 0 17:31 pts/1 00:00:00 -kshReview week ten lab assignmentIs there an orphan process listed below?root 1 0 0 2010 ? 00:03:17 initdandrear 22387 22385 0 17:34 pts/1 00:00:00 grepinitroot 927 1 0 2010 ? 00:08:58 /usr/sbin/sshdroot 22350 927 0 17:31 ? 00:00:00 sshd: dandrear@pts/1dandrear 22390 22385 0 17:34 pts/1 00:00:00 sort -rdandrear 22389 22385 0 17:34 pts/1 00:00:00 grepdandreardandrear 22388 26386 0 23:34 pts/1 00:00:00 ps -efdandrear 22385 22351 0 17:34 pts/1 00:00:00 /bin/ksh ./pid_ppid.sh dandreardandrear 22351 22350 0 17:31 pts/1 00:00:00 -kshReview week ten lab assignmentTerminate orphan Processeskill -3 8074 Signal the process with 8074 pid to “quit”kill -1 8074 Signal the process with 8074 pid to “hangup”kill -9 8074 Signal the process with pid 8074 to be “killed”Review week ten lab assignment/etc/rc.d/rc.sysinitThis init script performs basic system configuration which includes setting the system clock, hostname, and keyboard mapping; setting up the swap partitions; checking the remaining file system for errors; and turning on the quota management./etc/rc.d/rcThis init script runs the scripts for the services that need to be started when you first bring the system up and that need to be started or stopped when the system goes from single user mode to multiuser mode and back down again.Review week ten lab assignment/etc/rc.d/init.dThis init.d directory contains shell rc scripts and run via symbolic links in the /etc/rc.d/rcn.d directories, where n is the runlevel the system is entering. The following scripts reside in this directory./etc/rc.d/rc.localThis file is executed after the init scripts. Commands can be placed in this file to customize the system. These commands are best suited to execute in the background and after the initialization process completes.Review week ten lab assignment/etc/rc.d/rc1.d This directory contains scripts that start and stop during a specific run level. The following scripts execute during run level one (1): K10cups K25sshd K50netdump K74nscd K86nfslock K91isdn S01sysstatNotice the numbering from 00 to 99. This numbering provides positioning of a script within the whole scheme of execution.Review week ten lab assignment/etc/rc.d/rc1.d K01cmanic -> /etc/init.d/cmanic K01hprsm -> /etc/init.d/hprsm K03rhnsd -> ../init.d/rhnsd K05atd -> ../init.d/atd K05saslauthd -> ../init.d/saslauthd K10cups K10hpasm -> /etc/init.d/hpasm K10psacct -> ../init.d/psacct K15gpm -> ../init.d/gpm-> ../init.d/cupsWeek ten, eleven, & twelve expected outcomesUpon successful completion of this module, the student will be able to:
  • Manipulate user accounts.
  • Describe how cron is used to invoke repetitive processes.
  • Manipulate process structure including:
  • a) fork and execute b) Initialization process c) Background/foreground d) PS tool
  • Explain basic UNIX security issues.
  • Describe disk
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