linux crash course

Linux Crash Course Selected snippets from CIS52 Long ago, in a galaxy far away … • Computing power was costly – UNIVAC cost $1 million • CPU time was a premium – Most mainframes had less computing power than a calculator on the shelf at Wal-Mart • Jobs were submitted into a queue – Only one process at a time – scheduling nightmare What was needed • Allow multiple users to access the same data and resources simultaneously • Service many users more cheaply than buying each their own machine • The ability to run multiple processes at once • And so while maintaining user segregation and data integrity Enter Unix, pride of Bell Labs • Originally written in PDP-7 assembly language by Ken Thompson • To make it work on multiple architectures (portable), Thompson rewrote Unix in B • Dennis Ritchie developed C, and with Thompson, rewrote Unix in C What was so great about it? • • • • • Multiuser Multiprocess Non-proprietary Economical for business Initially given for free to colleges and universities (great tactic!) What happened? • UNIX became commercialized • Proprietary code, specialized distributions • Costs started to become a hindrance • So … let’s make our own Unix … GNU • Richard Stallman decides that there should be a free version of Unix available • Forms the GNU project – GNU’s Not Unix • Writes all of the system programs and utilities to mimic Unix variants • Everything but a kernel (Hurd) Final piece • Universities trying to teach Unix and OS design can’t afford Unix • Andrew Tanenbaum writes Minix • Linus Torvalds, dissatisfied with Minix, writes his own – Linux GNU-Linux • Torvalds has a perfectly functioning kernel – but no system programs • Finds a perfect candidate in GNU • Together, the operating system world was changed dramatically Why Linux? • • • • • Software Hardware Portability Standards $$$ Filenames con’t • Spaces and other special characters a bad idea • Instead of spaces use underscores or periods – Ex: my_file or my.file Hidden Files • To make a file hidden, start it with a period – Ex plan • A normal ls will not show hidden files • Use ls –a to reveal ALL files • Startup files, containing configuration settings for your account, hidden mkdir – create directory • Syntax: mkdir directory • Directory can be a relative or absolute pathname (we’ll get to that in a minute) • You can use ls –F to show directories with a forward slash at the end of the name • If using a color terminal, directories will be a different color than ordinary files Working Directory • The directory you are currently working in • pwd will tell you what your working directory is • Helpful to know when using relative pathnames (again, coming up) Home Directory • Not to be confused with working directory • The directory you start in when you first logon • Most users it is /home/username • For root, it is /root • Can be changed by system administrator cd – change working directory • Syntax: cd [directory] • Again, directory can be absolute or relative • If no argument given, changes working directory back to your home directory Absolute Pathnames (finally) • Absolute pathname for a file gives the file’s location relative to the root of the filesystem • Sometimes long • Ex: /home/jhowell/Assignment1/animals • Shortcut: ~ represents your home directory • So the above could also be ~/Assignment1/animals Relative Pathanmes • A pathname relative to the current working directory • Make sure you know what your working directory is! • Shorter • Ex, in my home directory: Assignment1/animals and Directories • is an alias for the working directory • is an alias for the parent of the current working directory • These pointers are placed in every directory when created by mkdir • Can be used in relative pathnames Common Directories • • • • • • • / (root) – root of the filesystem /bin – essential system binaries (commands) /boot – files for the bootloader /dev – device files /etc – system configuration files /home – user home directories /lib – standard libraries and modules Common con’t • /mnt – mount point for temporary filesystems (floppies, CD-ROMs, non-native partitions) • /opt – optional add-on software • /proc – kernel and process information • /root – root’s home directory • /sbin – essential system binaries • /tmp – temporary space (not swap) Common con’t • /usr – common area for data / program users use frequently • /var – frequently changing data like system logs, caches, spools and mailboxes • That said, all these can reside on the same partition • Only / and a swap partition required Permissions • Use a ls –l (for long view) and you might see something like this: drwxr-xr-x -rw-rw-r-drwxrwxr-x jhowell jhowell 4096 Aug 18 15:46 Desktop jhowell jhowell Sep 18:08 myfile jhowell jhowell 4096 Aug 22 15:32 public_html # of links Type of file File Permissions filename group user size Date and time created / accessed chmod – CHange MODe • Changes permissions • Syntax: chmod [ugoa][+-][rwx] • Ex: grant everyone (all) read and write chmod a+rw myfile • Ex: remove execute permission for other chmod o-x myfile Permissions Caveats • To execute a shell script you must allow both read and execute permissions • To get into a directory, you must have execute permission • root can still read and write to files without read and write permissions ... Linux GNU -Linux • Torvalds has a perfectly functioning kernel – but no system programs • Finds a perfect candidate in GNU • Together, the operating system world was changed dramatically Why Linux? ... a virtual terminal to the server • telnet, ssh, X Windows • Most common way to interact with a Linux/ UNIX machine • Ubuntu – Applications->Accessories->Terminal The Shell • Command interpreter... commands issued by user into commands sent to the kernel • Common shells: bash, tcsh, csh, zsh, ksh • Linux default is bash (Bourne Again Shell) Administrative privleges • • • • root or superuser Full