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unix - Why Learn Unix(or its variations Many Unix...

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Why Learn Unix (or its variations)? Many Unix systems (Solaris on Sun workstations, IRIX on SGI workstations, AIX on IBM servers, various versions of Linux on PCs, FreeBSD, OpenBSD) Unix provided the basis (since 1970s) for many operating system concepts and features (multi-tasking, shell and scripting, hierarchical file systems) Apple Computer’s Mac OS X is Unix-based, see a wikipedia article , and a brief Unix timeline Mac OS X and Unix articles (tutorial, advanced Unix, how- to’s) The Law Enforcement and Forensic Examiner's Introduction to Linux , v.3.65 by Barry J. Grundy
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Layered Structure of the Unix/Linux Operating System: Applications (GUI, web browser, word processor, ftp, etc.) Shells (sh, bash, csh, tcsh, etc.) Language libraries (C, Java, Ada, FORTRAN) System calls (open, close, fork) Unix kernel: File system, process manager, memory manager, CPU scheduler Device drivers Hardware (CPU, RAM, BIOS, hard disk, CD-ROM, monitor) Application User Interface (AUI) Application programmer’s Interface (API) Operating System
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Unix file systems: The Unix operating system started out as a file system. All system entities are considered as files, including regular files (text or binary), directories, devices, links, pipes, and sockets. A typical file system tree looks as follows: / (root) bin boot dev etc home lib lost+found mnt opt proc root sbin tmp usr var /bin – binary (executable) images of commands such as cat, chmod, cp, kill, ls, mkdir, mv, ps, pwd, rm, rmdir, su, vi /boot – image of kernel to boot the system /dev – devices (special files) including character special and block special
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/etc – configuration information /home – user home directories /lib – language libraries for C, C++, Java, Ada, FORTRAN /lost+found files not connected to other directory, which are found using the tool fsck (file system check) /mnt mount points for other file systems such CD-ROM, floppy, using the mount command /opt – add-on packages /proc – process (task) information /root – information about the root (administrator) account /sbin system administration tools such as init, shutdown /tmp temporary files used by several commands (e.g. editor) /usr contains subdirectories bin, doc, include, lib, local, man, src, tmp, shared by all users /var – variable data such as incoming mail
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How are files represented and saved on disk: 1076 syllabus.txt 2085 lab1.c 20345 lab2.java Contents of directory ~/courses inode table file type number of links file mode user ID group ID creation time modification time access time disk address inode for file lab1.c inumber file name disk drive
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Common Unix shells and commands: shells with increasing functionality: sh (Bourne shell) Æ bash (Bourne again shell, used in Linux) ksh (Korn shell) Æ zsh csh (C shell) Æ tcsh (TC shell) File-related commands: ls (list contents of directory, similar to dir in DOS, options include -l for long format, -a to show all files, -R to show files in the entire directory tree, -t to show last modified file first) cat (concatenate and display file, e.g. cat lab1.c)
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