Presentation Transcript

1. Agenda Administrative Issues Link of the Week This Week’s Expected Outcomes Points of interest Moving around in UNIX Break-Out Problems Upcoming Deadlines Hands-on Information Lab Assistance, Questions, and Answers
2. Announcements There is no script logic for Lab Assignment 12-1 and 12-2. Open source presentations (Section V1FF) on April 14, 2014. Announcements
3. Domain name registration Web site https://www.pairnic.com/services.html?gclid=COXiuLv6mI0CFSCTWAod81M57A Determine if a domain is currently in use. http://www.pair.com/ Online success starts with a great domain. What is a domain name? A domain name (for instance, "example.com") is an identification string that defines a realm of administrative autonomy, authority, or control on the Internet. Domain names are formed by the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name. Link of the week
4. What is the function of the Domain Name System? The DNS translates Internet domain and host names to IP addresses. DNS automatically converts the names we type in our Web browser address bar to the IP addresses of Web servers hosting those sites. Link of the week
5. What is the function of the Domain Name System? The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates easily memorized domain names to the numerical IP addresses needed for the purpose of locating computer services and devices worldwide. By providing a worldwide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet. Link of the week
6. BIND (Berkley Internet Name Domain) BIND is the most widely used DNS software on the Internet. On Unix-like operating systems it is the de facto standard. Originally written by four graduate students at the Computer Systems Research Group at the University of California, Berkeley (UCB), the name originates as an acronym from Berkeley Internet Name Domain,[5] reflecting the application's use within UCB. Link of the week
7. What is meant by top level domain? A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last label of a fully qualified domain name. Link of the week
8. Top Level Domain (TLD) gov – Government edu – Educational org – Other organizations ( often nonprofit) mil – Military com – Commercial business net – Network organizations ca – Canada th – Thailand Link of the week
9. Link of the week
10. Who owns the Internet root? The authoritative name servers that serve the DNS root zone, commonly known as the “root servers”, are a network of hundreds of servers in many countries around the world. They are configured in the DNS root zone as 13 named authorities, as named on the next slide. Link of the week
11. Who owns the Internet root? VeriSign, Inc. University of Southern California (ISI) Cogent Communications Internet Systems Consortium, Inc University of Maryland NASA (Ames Research Center) US Department of Defence (NIC) US Army (Research Lab) Netnod VeriSign, Inc. RIPE NCC ICANN WIDE Project Link of the week
12. Who owns the Internet root? http://www.iana.org/domains/root/servers Link of the week
13. Who is ICANN? Today, the Internet Corporation for Assigned Names and Numbers (ICANN) is one of several managers of the top-level development and architecture for Internet domain name space. It authorizes domain name registrars, through which domain names may be registered and reassigned. Link of the week
14. Top level domain name The right-most label conveys the top-level domain; for example, the domain name www.example.com belongs to the top-level domain com. The hierarchy of domains descends from the right to the left label in the name; each label to the left specifies a subdivision, or subdomain of the domain to the right. For example: the label example specifies a node example.com as a subdomain of the com domain, and www is a label to create www.example.com, a subdomain of example.com. Link of the week
15. IANA - Internet Assigned Numbers Authority The top-level domains (TLDs) such as com, net and org are the highest level of domain names of the Internet. Top-level domains form the DNS root zone of the hierarchical Domain Name System. Every domain name ends with a top-level domain label. Each country has an ISO (International Organization for Standardization) country code designated as its domain name. Link of the week
16. Hostname A hostname is a domain name that has at least one associated IP address. For example, the domain names www.example.com and example.com are also hostnames, whereas the com is not a domain. However, other top-level domains, particularly country code top-level domains, may indeed have an IP address, and if so, they are also hostnames. Link of the week
17. Hostname Hostnames impose restrictions on the characters allowed in the corresponding domain name. A valid hostname is also a valid domain name, but a valid domain name may not necessarily be valid as a hostname. Link of the week
18. UNIX-like file systems UNIX-like file system is hierarchical. It is interpreted from left to right. The top-level domain name appears at the left end. /var/mail/dandrear The URL (Uniform Resource Locator) is also hierarchical. Its top-level domain name appears at the end, but is read from right to left. alpha.einstein.edu beta.ca.mail2web.com Link of the week
19. Upon successful completion of this module, the student will be able to: User initialization Crontab File System and disks Action words in /etc/inittab file This Week’s Expected Outcomes
20. User Initialization /etc/profile file is the basic setup for all users. The /etc/profile contains the environmental variables and commands used by most shell users. User preferred environmental set up $HOME/.profile $HOME/.bash_profile If the /etc/profile and .profile files are not present during the initialization, a prompt is still displayed. Use the ls –a command to display the .profile or .bash_profile file under your $HOME directory. UNIX Operating System
21. Metadata Metadata is data about data. It may describe a single piece of data or multiple content items and hierarchical levels. Example: Legacy card catalogs in a library. Metadata can be the name of a US corporation, or a registered trademark. UNIX Operating System
22. Metadata Metadata is structured information that describes and allows us to find, manage, control and understand other information. Structured metadata represents the specifications of this information. In this case, a better definition of this design concept would be "data about the containers of data". UNIX Operating System
23. Metadata There are many different types of metadata. Business Intelligence metadata General IT metadata IT metadata management products File system metadata Image metadata UNIX Operating System
24. /etc/inittab actions respawn – The process will be restarted whenever it terminates. wait – The process will be started once when the specific runlevel is entered. once – The process will be executed once when the specific runlevel is entered. boot – The process will be executed during system initialization. initdefault – This entry specifies the runlevel which should be entered after system boot. sysinit – The process will be executed during system boot. It will be executed before any boot or bootwaitentries. UNIX Operating System
25. /etc/inittab Actions powerwait – The process will be executed when the power goes down. powerokwait – This process will be executed as soon as init process is informed that the power has been restored. powerfailnow – This process will be executed when the init process is informed that the battery of the external UPS power is failing. ctraltdel – The process is executed when the init process receives the SIGINT signal. This means that someone on the system console has pressed the Ctrl-Alt-Del key combination. UNIX Operating System
26. UNIX-like commands ps –s (view zombie processes) ps –e –o pid,ppid,stat (display all processes / listed fields) ps –aux (view status of all processes) ps –x (view only active processes) ls –a (view “.” processes) ps -aux | grepcrond (view crond executing) nice (UNIX) (modified scheduling priority) (-20 to 19 range) If a user wanted to compress a large file, but not slow down other processes, they might run the following: nice -n 19 tar cvzf archive.tgz largefile UNIX Operating System
27. UNIX-like commands umask (displays umask numeric values) umask –S (displays umask symbolic values) fg (Continues a stopped job by running it in the foreground, some shells are not able to run this command ). bg (Continues a stopped job in the background) cat /etc/shells (Display available shells on system). echo $SHELL (Display current shell being utilized). chsh –s /bin/ksh (Change to a different shell) printenv (command to display environment variables). df (report file system disk space) UNIX Operating System
28. Unix/Linux ProcessesLinux defines a unit of work as a task or process. UNIXdefines a unit of work as a process. Each process is identified by a unique PID (Process ID). Each user is identified by a unique UID (User ID). Each group of users is uniquely identified by a GID (Group ID). Each process is started from a previous process using the fork and exec command. The init process is created by the kernel using a non-traditional procedure called hand-crafted or spontaneous. UNIX Operating System
29. Non-Inherited Parent Process Attributes File locks (semaphores) Child resource utilization is set to zero Pending signals (kill –l signals) Daemon processes Offer services like web pages serving, email transferring, time synchronization, and similar. They usually consume little CPU and memory, and run quietly without user interaction. They mainly communicate with other computer programs, or with other computers via network. UNIX Operating System
30. Linux Kernel Modules Hardware in Linux is handled by kernel drivers, many come from kernel modules. These are stand driver files, which are stored in the /lib/modules directory. Typically, Linux loads the needed modules at boot time. UNIX Operating System
31. Modules loaded on system using lsmod command Module SizeUsed by lsofs 35820 0 zlib_inflate 21888 1 isofs floppy 65200 0 fat 49536 1 vfat vfat 15680 1 cdrom 39080 2 sr_mod, ide_cd UNIX Operating System
32. Loading Kernel Modules Linux allows loading kernel modules with two programs: insmod and modprobe. The insmod program loads a module into the kernel. The process requires that you have already loaded any modules on which you’re loading relies. The modprobe program automatically loads any dependent modules. UNIX Operating System
33. Loading Kernel Modules Examples: lnsmod /lib/modules/3.7.33/kernel/block/floppy.ko (extension is required) When executing the insmod program, if it fails during the download of floppy.ko, chances are some dependencies are needed. You can manually download the dependent modules or execute the modprobe program. modprobe floppy (extension not required) The –n or –dry-run option causes modprobe to perform checks and all other operations except the actual download. UNIX Operating System
34. CrontabUtilization Cronis the periodic event scheduler of your system. cron enables users to schedule jobs (commands or shell scripts) to run periodically at certain times or dates. It is commonly used to automate system maintenance or administration, though its general-purpose nature means that it can be used for other purposes, such as connecting to the Internet and downloading email. The following examples give you an idea of its usefulness and necessity. regular daily backups periodic mail checking polling a device(s) for input sending regular reports sending user email every time a cron function is performed UNIX Operating System
35. CrontabUtilization cron file locations /etc/crontab /etc/cron.deny /etc/cron.allow Typical directory configuration /etc/cron.d/hourly /etc/cron.d/daily /etc/cron.d/weekly /etc/cron.d/monthly UNIX Operating System
36. How frequent does crond execute on Unix-like systems? Disable email To prevent email messages from being sent to your mail account, create a record that contains the following syntax: * * * * * echo dandrear@franklin.edu > trash_bin To cancel the email redirection, enter the following: rmtrash_bin If the output is not needed, the following syntax can be included: * * * * * echo “Hello Administrator” > /dev/null 2>&1The /dev/null device is a special file that disregards all data written to it. UNIX Operating System
37. crontab restrictions If your name appears in the cron.allow file. If that files doesn’t exist, you can use crontab. If your name does not appear in the cron.deny file. If cron.deny exists and is empty, all users can use crontab. If neither file exists, only the root user can use crontab. UNIX Operating System
38. Samba The /etc/samba/smb.conf file controls most aspects of how Samba works and is divided into two sections. Each section begins with a line starts with an open bracket ([), includes text, and ends with a closed bracket (]). UNIX Operating System
39. [globals] Defines global parameters [printers] Defines printers [home] Defines shares in the homes directory Comments in the smb.conf can start with either a pound (#) or (;). # A private directory, usable only by Bob. ; [bobsdir] ; comment = Bob’s Service ; path = /usr/somewhere/in/space ; writeable = yes ; printable = no ; public = no UNIX Operating System
40. What is the functionality of Network File System (NFS)? It is a remote file system designed by Sun Microsystems, available on computers from most UNIX system vendors. It allows the server to share selected local directory hierarchies with client systems on heterogeneous network. Files on the remote computer (fileserver) appear as if they are present on the local system. The physical location of a file is irrelevant to an NFS user. UNIX Operating System
41. Network Services A variety of services available across a network NFS: Developed by Sun Micro Systems Runs on UNIX, DOS, Windows, VMS, and Linux Files on the remote computer appear as if they are present on the local system. Server configuration - /etc/exports file is the main NFS configuration file and it consists of two columns: Column #1 - lists the directories the network or DNS domains the can get access to the directories. Column #2 – lists NFS options in brackets. #/etc/exports/data /files *(ro,sync) /home 192.168.1.0/24 (rw,sync) /data/test *.my-site.com (rw,sync) /data/database 192.168.1.203/32 (rw,sync) UNIX Operating System
42. Network Services A variety of services available across a network NFS: Use the chkconfig command to configure the required NFS daemons to start at boot. Use exportfs –a command when no directories have been exported to NFS. Use exports –r command when adding a shared directory to export only the new entries. Use the showmount –a command to list all currently exported directories. In the /etc/fstab file, add a similar entry: #/etc/fstab 192.168.1.100:/data/files /mnt/nfsnfssoft,nfssvers=2 o 2 UNIX Operating System
43. Network Services Remote (rlogin) is a UNIX command that allows an authorized user to login to other UNIX machines (hosts) on a network and to interact as if the user were physically at the host computer. Once logged in to the host, the user can do anything that the host has given permission for such as read, edit, or delete files. SSH is a protocol that allows computers to communicate with each other over encrypted connections. An SSH client is used to log in to a remote machine (running an SSH server) and allows the execution of commands on that machine. UNIX Operating System
44. Is there an orphan process? root 1 0 0 2011 ? 03:20:28 /sbin/init dandrear 13087 13085 0 22:26 pts/3 00:00:00 grepinit root 11856 9595 0 21:13 ? 00:00:00 sshd: dandrear [priv] root 11406 9595 0 20:58 ? 00:00:00 sshd: dandrear [priv] root 10542 9595 0 20:18 ? 00:00:00 sshd: dandrear [priv] dandrear 13090 13085 0 22:26 pts/3 00:00:00 sort -r dandrear 13089 13085 0 22:26 pts/3 00:00:00 grepdandrear dandrear 13088 13085 0 22:26 pts/3 00:00:00 ps -ef dandrear 13085 11427 0 22:26 pts/3 00:00:00 /bin/ksh ./pid_ppid.sh dandrear dandrear 13074 1 0 22:26 pts/4 00:00:00 client_ser dandrear 11859 11858 0 21:13 pts/4 00:00:00 -ksh dandrear 11858 11856 0 21:13 ? 00:00:00 sshd: dandrear@pts/4 dandrear 11427 11426 0 20:59 pts/3 00:00:00 -ksh dandrear 11426 11406 0 20:59 ? 00:00:00 sshd: dandrear@pts/3 dandrear 10548 10547 0 20:18 pts/2 00:00:00 -ksh dandrear 10547 10542 0 20:18 ? 00:00:00 sshd: dandrear@pts/2 UNIX Operating System
45. X-11 X-11 is the name of the window manager used for most UNIX and Linux operating systems. A window manager is software that interfaces the video, keyboard and mouse drivers together to allow the user to communicate with the computer via a GUI. X-11 is unique in the sense that it runs over a network connection, specifically over IP. This enables a remote user to use his or her local X-Windows environment to interact directly with the other computer’s window manager as if they were sitting on that machine. UNIX Operating System
46. X-11 X-11 uses a client-server model, where the window manager is the server, and the user is using various clients. Applications that can be run in the graphical user interface are often written to use the X-11 software libraries to enable them to be used remotely. This is one of the strengths and power of the Unix system. X-11 enables a remote system to treat your local computer, it screen, keyboard and mouse as just another set of terminal interface devices that use an X-11 driver to communicate with the X-Windows manager. UNIX Operating System
47. Disk and File System Structure Copy-on-Write It is an optimization strategy for multiple users can give the same pointer for a resource. The primary advantage is that if a caller never makes any modifications, no private copy is needed. This strategy is used in virtual memory operating systems pages in memory that might be modified by either the process or its copy are marked copy-on-write. UNIX Operating System
48. Disk and File System Structure It is an organization of data and metadata on a storage device. It is the methods and data structure that an operating system uses to keep track of files on a disk or partition; that is the way the files are organized on the disk. Think of a file system as a protocol. File systems give meaning to the data on a particular storage device. UNIX Operating System
49. UNIX Operating System
50. UNIX Operating System
51. UNIX base root file system tree structure /bin (commands) /dev (devices) /etc (system configuration/executables) /sbin (boot commands) /usr/sbin (administrative commands) /home (users home directories) /lib (shared libraries) /mnt (temporary mount directory) /opt (optional software) /proc (processes) /stand (boot-related files) /var (spooling) UNIX Operating System
52. lost+found directory The fsck utility is generally able to repair most system damage and the frequency with which you will find anything at all in your lost+found directories has slowed significantly If you have a system crash and the Linux file system checker (fsck) recovers corrupt files they are placed here. UNIX Operating System
53. Unix-like System Security Security on UNIX-like systems has focused on the following areas: Files and directories umask PATH variable SELinux iptables TCP Wrapper chroot jail password authentication UNIX to UNIX commands One-way function UNIX Operating System
54. Disks versus File Systems Application(s) interface with file systems and not disks. Why? Because disks have shortcomings and are not responsible for data recovery. File systems must return the stored data to a consistent state after an unplanned system crash. UNIX Operating System
55. File System Data recovery Data loss Fsync system call The fsync() function requests that all data for the open file descriptor named by fildes is to be transferred to the storage device associated with the file described by fildes. The nature of the transfer is implementation-defined. The fsync() function shall not return until the system has completed that action or until an error is detected. UNIX Operating System
56. File System Track caching Shortcoming of track caching – the file system expects the data to be stable store. A system crash with data in the cache will not deliver the user application integrity that was promised. Ways to circumvent this shortcoming – use non-volital memory and provide microcode restart after power failures. UNIX Operating System
57. The problem with using non-volatile memory and microcode restart is the cost. This solution is the disk controller, but is rarely an option. Newer Disks Provide tag queuing – each request passed to the disk driver is assigned a unique number. Most disk controllers can accept at least 16 pending requests. In combination, the fsync and tag queuing are combined. Tag queuing was first implemented in SCSI disks. Enabling both reliability and speed. ATA disks lacked tag queuing. Later ATA adopted a tag queuing called Tag Command Queuing (TCQ). UNIX Operating System
58. Serial ATA has a new definition called Native Command Queuing (NCQ) that has a bit set in the write command that tells the drive if it should report completion when media has been written or when cache has been hit. If the driver correctly sets this bit, then the disk will display the correct behavior. Disk Sector Size From 1950s to 2010 the disk sector size was 512. In 2010, the sector size was increased to 4,096. Problems associated with this retrofit Error rate per bit has risen, requiring the use of ever longer correction codes. The error code must have enough redundancy for each sector to handle a high correction rate even though most sectors will not require it. UNIX Operating System
59. Is the increase density worth the extra overhead? Sectors are 8 times larger, which eliminates 88% of the sector start and stop headers. You want to reduce the number of non-data bits on the disk. In effect, using 4,096 byte sectors doubles the amount of user data that can be stored on a given disk. Legacy File Systems The 4,096-byte sectors have to emulate the old 512-byte sector disks. This mode causes the disk to be at least 50% slower. UNIX Operating System
60. How to avoid the slowdown Files smaller than or equal to 512-bytes are accumulated in a 4,096-byte block. Conclusion Your file system must know the type of disk technology to which they are running to ensure reliable data retrieval and performance. Use flash-memory technology! UNIX Operating System
61. Points of interest A USB can be a bit challenging for operating systems designed as a hot-pluggable device. The Linux kernel was not originally designed to handle this type of technology. The kernel relies on external utilities to help manage matters. Two tools are used to help manage USB devices: usbmgr and hotplug. UNIX Operating System
62. lsmod – is a program to show the status of modules in the Linux kernel. insmod – is a simple program to insert a module into the Linux Kernel modprobe – is a program to add and remove modules from the Linux Kernel lsusb - list USB devices Moving Around in UNIX
63. 1. How often do the following two commands execute? # 1.1. This is a comment. * * * * * c:\tools\CheckForNewFiles.exe # 1.2. This is a comment. * * 3 * * c:\tests\backup.bat 2. Define: File System Super block 3. What application is BIND associated 4. What is the “lost+found” area considered on a Unix-like system? 5. Linux Virtual File System 6. One-Way Encryption or One-Way Function 7. Compare a block device to a character device Break-out problems
64. Lab Assignment 11-1,Knoppix File System due March 24, 2014 Lab Assignment 12-1, 12-2 Programming Assignment 2 /Archives due March 31, 2014 Lab Assignment 13-1Open Source presentation due April 14, 2014 Lab Assignment 14-1 CGI Script April 19, 2014 Hands on information
65. Questions Comments Concerns I am available after this Franklin Live session to discuss any problems and/or concerns regarding the lab assignments After class assistance
66. Lab Assistance available by phone and/or email