Unix fundamentals

Unix fundamentals

• 1.
  Unix Basics Prepared by Dima Gomaa
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  What Is anOperating System? • Interface between Users and the Hardware • Take care of Storage Management • Take care of I/O device management
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  History of theUNIX Operating System 1969 AT&T Bell Labs UNICS system -designed by Ken Thompson & Dennis Ritchie 1970 UNICS finally became UNIX 1973 UNIX rewritten in C, making it portable to different hardware Mid 1970s University of California at Berkeley (BSD) contributed many important features like vi, C shell etc. 1982 AT & T came back and started commercial production- Editions ->Systems Late 1980s AT & T released SVR4 unification of SV3.2,BSD,SunOs & XENIX 1991 Linux from Linus Torvalds 1990s POSIX Standard, MIT introduced X-Windows 3
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  UNIX Architecture –Kernel & Shell User Shell Kernel Hardware 4
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  More Features ofUNIX • Hierarchical file system • Multi tasking • Multi user • Pattern matching (wildcard characters) • Programming facility • Documentation 5
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  Command Line Format Syntax: $ command [-options] [arguments] 1. Separation 2. Order 3. Multiple options 4. Multiple arguments 6
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  Basic Commands(1)  ls list files and directories  ls -a list all files and directories  mkdir make a directory  cd directory change to named directory  cd change to home-directory  cd ~ change to home-directory  cd .. change to parent directory  pwd display current dir path  useradd add new user in the system  usermod modify user  userdel delete user  groupadd add new group in the system
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  Basic Commands(2)  cp file1 file2 copy file1 and call it file2  mv file1 file2 move or rename file1 to file2  rm file remove a file  rmdir directory remove a directory  cat file display a file  more file display a file a page at a time  who list users currently logged in  lpr -Pprinter psfile print postscript file to named printer  * match any number of characters  ? match one character  man command read the online manual page for a command
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  Basic Commands(3)  command > file redirect standard output to a file  command >> file append standard output to a file  command < file redirect standard input from a file  grep 'keyword' file search a file for keywords % grep science science.txt  wc file count number of lines/words/characters in file % wc -w science.txt  sort sort data (numerically or alphabetically) Ex: to sort the list of object, type % sort < biglist and the sorted list will be output to the screen.
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  The File SystemHierarchy / usr etc home dev var tmp bin sbin dsk rdsk adm sadm ls who 10
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  File Path name Asequence of file names, separated by slashes (/), that describes the path, the system must follow to locate a file in the file system Absolute pathname (start from the /-directory): Eg: /export/home/user1/file1 Relative pathname (start from the current directory) ./test1 (. = current directory) ../team03/.profile (.. = parent directory) 11
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  File Characteristics $ls -l -rw-r--r-- 1 user3 class 37 Jul 24 11:06 f1 -rwxr-xr-x 1 user3 class 52 Jul 24 11:08 f2 drwxr-xr-x 2 user3 class 1024 Jul 24 12:03 memo File Links Group Name Type Timestamp Owner Size Permissions 12
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  Who can accessa File? The UNIX system incorporates a three-tier structure to define who has access to each file and directory: user The owner of the file group A group that may have access to the file other Everyone else • The ls -l command displays the owner and group who has access to the file. $ ls -l -rw-r--r-- 1 user3 class 37 Jul 24 11:06 f1 -rwxr-xr-x 1 user3 class 37 Jul 24 11:08 f2 drwxr-xr-x 2 user3 class 1024 Jul 24 12:03 memo | | owner group 13
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  File system security(access rights) -rwxrwxrwx a file that everyone can read, write and execute (and delete). -rw------- a file that only the owner can read and write - no- one else can read or write and no-one has execution rights (e.g. your mailbox file).
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  Unix File Permissions  File type, owner, group, others drwx------ 2 jjoshi isfac 512 Aug 20 2003 risk management lrwxrwxrwx 1 jjoshi isfac 15 Apr 7 09:11 risk_m->risk management -rw-r--r-- 1 jjoshi isfac 1754 Mar 8 18:11 words05.ps -r-sr-xr-x 1 root bin 9176 Apr 6 2002 /usr/bin/rs -r-sr-sr-x 1 root sys 2196 Apr 6 2002 /usr/bin/passwd  File type: regular -, directory d, symlink l, device b/c, socket s, fifo f/p  Permission: r, w, x, s or S (set.id), t (sticky)
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   chmod [options] file change access rights for named file For example, to remove read write and execute permissions on the file biglist for the group and others, type % chmod go-rwx biglist This will leave the other permissions unaffected. To give read and write permissions on the file biglist to all, % chmod a+rw biglist
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  Default Permissions The defaultprotections for newly created files and directories are: File -rw-r—r-- 644 Directory drwxr-xr-x 755 These default settings may be modified by changing the umask value. 17
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  umask - PermissionMask Umask specifies what permission bits will be set on a new file or directory when created. New Directory: 777 – 022 755  rwxr-xr-x New File : 666 – 022 644 rw-r—r— The default value of umask is set in /etc/profile. This can be changed for all the users or a particular user 18
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  chown - ChangeFile Ownership Syntax: chown owner [:group] filename ... Changes owner of a file(s) and, optionally, the Example: group ID $ id uid=101 (user1), gid=101 (group1) $ cp f1 /tmp/user2/f1 $ ls -l /tmp/user2/f1 -rw-r----- 1 user1 group1 3967 Jan 24 13:13 f1 $ chown user2 /tmp/user2/f1 $ ls -l /tmp/user2/f1 -rw-r----- 1 user2 class 3967 Jan 24 13:13 f1 Only the owner of a file (or root) can change the ownership of the file. 19
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  The chgrp Command Syntax: chgrp newgroup filename ... Example: $ id uid=303 (user3), gid=300 (class) $ ls -l f3 -rw-r----- 1 user3 class 3967 Jan 24 13:13 f3 $ chgrp class2 f3 $ ls -l f3 -rw-r----- 1 user3 class2 3967 Jan 24 13:13 f3 $ chown user2 f3 $ ls -l f3 -rw-r----- 1 user2 class2 3967 Jan 24 13:13 f3 20
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  su - SwitchUser Id Syntax: su [user_name] Change your effective user ID and group ID Example: $ ls -l f1 -rwxr-x--- 1 user1 group1 3967 Jan 24 23:13 class_setup $ id uid=303 (user1), gid=300 (group1) $ su – user2 Password: $ id uid=400 (user2), gid=300 (group1) 21
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  Special File Permissions– setuid, setgid, sticky bit  setuid – changes the effective user id of the user to the owner of the program  chmod u+s f1 or – chmod 4744 f1  setgid – changes the effective group id of the user to the group of the program  chmod g+s f1 or  chmod 2744 f1  sticky bit – ensures the deletion of files by only file owner in a public writable directory  chmod +t f1 or  Chmod 1744 f1 22
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  What Is vi? • A screen-oriented text editor • Included with most UNIX system distributions • Command driven • Categories of commands include – General administration – Cursor movement – Insert text – Delete text – Paste text – Modify text 23
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  Starting and Endinga vi Session vi [filename] Start a vi edit session of file Example: $ vi testfile - If the file doesn’t exist, it will be created - Otherwise vi will open the existing file All modifications are made to the copy of the file brought into memory. :wq or :x or <shift-zz> write and quit :w write :q quit :q! Quit without saving 24
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  Cursor Control Commands 1G <ctrl-b> H k <up-arrow> 0 $ b,B w,W h l <left-arrow> <right-arrow> <down-arrow> j L <ctrl-f> G 25
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  Input Mode: i,a, O, o i will insert character at the present cursor position I will insert character at the beginning of the line a will append character at the present cursor position A will append character at the end of the line o will insert a blank line below O will insert a blank line above 26
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  Deleting Text: x,dw, dd, dG x deletes the current character dw deletes the current word dd deletes the current line dG delete all lines to end of file, including current line. With any of these you can prefix a number Example: 3dd will delete 3 lines d$ to delete to the end of the line d0 to delete to the start of the line 27
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  Copying, moving and changing Text yy copy the line yw copy the word p will paste the yanked lines below dw cut the word P will paste the yanked lines above dd cut the line r will overwrite the current character R will replace all text on the right of the cursor position cw will replace only the current word 28
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  Searching for Text:/, n, N /director will locate for the first occurrence of the pattern ‘director’ n to locate the next occurrence N to locate the previous occurence 29
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  Monitoring Process The pscommand dislays process status information $ ps -f UID PID PPID ... TTY ... COMMAND john 202 1 ... tty0 ... -ksh john 204 202 ... tty0 ... ksh john 210 204 ... yyu0 ... ls -R / john 212 204 ... tty0 ... ps -f 30
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  Shell Scripting  Shell scripting skills have many applications, including:  Ability to automate tasks, such as  Backups  Administration tasks  Periodic operations on a database via cron  Any repetitive operations on files  Increase your general knowledge of UNIX  Use of environment  Use of UNIX utilities  Use of features such as pipes and I/O redirection
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  Examples of ShellScripting  Store the following in a file named simple.sh and execute it #!/bin/sh # Show some useful info at the start of the day date echo Good morning $USER cal last | head -6  Shows current date, calendar, and a six of previous logins  Notice that the commands themselves are not displayed, only the results