Working with the Unix OS

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Unix Administration New Software ! Purchasing For major equipment & software purchases ask to see things working before you commit yourself. This includes hardware AND software. ! Installing - Backup previous version of system - Installation may need root privileges. If shareware or network software – use source code from moderated news groups. - Keep software packages in separate directories to handle future releases. - Test basic features. - Check software works in non-privileged accounts. - Liaise with customer support from company supplying the software if problems occur. $ IS YOUR SYSTEM HUNG? A hung system is kernel resident with no kernel activity. Down and disabled system is kernel active but no results. A dead system the kernel has gone, processes are stopped. $ FILES THAT WOULDN'T DIE foo^H^H^Hbar, *, "- *", other assorted control sequences rm -i ? # confirmation for a single character file ls -ilb * # list strange file names od -xc # octal dump of parent directory clri # clear an inode /etc/unlink # or system call $ WON'T WORK Common problems that usually appear when a user complains "the system does not work properly". e.g. pr .profile | lp # no longer works The x bit has been removed for the owners home directory e.g. System administrator performs chmod 666 recursively from root, thus no traversal privileges - end of system. $ NO DISK SPACE df –t # show no disk free sed -n '$p' /usr/spool/console/May19 # print last line find / -type f -size +100000c –print # find large files (fuser -uk /dev/dsk/0s5; umount /dev/dsk/0s5) fsck /dev/dsk/0s5 # no errors now The in-core inode table had been corrupted $ TERMINAL WON'T GET PAST LOGIN Warning some terminals have the ability to map characters. If in doubt reset back to factory defaults first. tset -m ansi:ansi -m tvi910:910 # BSD command echo AT > /dev/tty03 # possible problem ls -l /dev/tty?? # may reveal a nondevice remove it and make device knowing major and minor numbers mknod /dev/tty03 c 1 3 # remake device 199
Unix Security 15. UNIX SECURITY Philosophy of Security ! Computer systems must be accessible - easy to access ("open") - able to communicate with other hosts ! Trade off between openness & security ! Depends on attitudes of administrators and users - an investment by both ! Unix tries to be more open. Full on-line manuals, Unix source available ! Experience has shown that non disclosure of information does not assure security. ! Unix philosophy is to be more open so that security holes are found and fixed! Unix Super User ! User "root" - Has access to everything - Can change permissions of anything - Use with caution - not for beginners - Minimum of 6-12 months experience - Double check everything "root" account used to install software, configure system, backing up, managing accounts etc. Password Security - Minimum of 6 chars (Unix allows 8 chars) - Not personal (e.g. girl/boy-friend name) - Never dictionary words - Include non-alphabetic characters or mixed upper/lower case (any printable character) - Can be remembered without writing down e.g. 1st letters of a sentence - Different for computer different systems - Change regularly (but not predictably!) - Don't reuse old passwords - always invent a new one. - Don't write it down or store it in the function keys of your terminal. Password File: /etc/passwd ! Readable by anyone !!! But passwords encrypted ! Passwords are encrypted and then compared with the correct encrypted password in /etc/passwd. ! Modern systems put a ! in the password field and store the encrypted password in a protected file called /etc/shadow. ! Maps user-name to uid number. ! Text file, one line per user (a record). Each record field is separated by a colon ":". Examples: user name:encrypted password:user uid:group gid: name, room, phone comment:home dir: login shell: root: h6H9fs*k: 0: 1: Super User: /root: /bin/sh lpstat: : 10: 10: : : /usr/bin/lpstat accts: f7J8gs6/: 80: 100: Accounts: /tmp: /db/accmenu fred: Ef5g7sG3: 500: 300: Fred Hill,A501,1900: /user/fred: /bin/sh ! Super user account (UID is zero) ! No command shell, only access to the Accounting system provided the accounting system can't create a shell. ! No password, shows status of line printer queue Group File: /etc/group - Similar to /etc/passwd - Maps group names to group ID numbers - Specifies group members other than those implied by the GID stored in /etc/passwd 200
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UNIVERSITY OF ATHENS DEPARTMENT OF
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Figure 27. Driver Entry Points.....
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Introduction to Unix ! Execution ma
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Introduction to Unix It works in th
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Introduction to Unix * matches 0 or
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Introduction to Unix vi file-name s
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Introduction to Unix 1,$s/^/>>/ 1,$
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Introduction to Unix ! Special Devi
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Introduction to Unix Working with F
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Introduction to Unix ! Communicatio
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Unix Shells 2. UNIX SHELLS Back Quo
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Unix Shells ! CASE Statement case t
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Unix Shells two lines !Y@Y@Z@Z@ZY c
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Unix Shells if $append then tee -a
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C Programming - Basics main() { int
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C Programming - Basics e.g. i += 2
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External Variables A C program cons
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C Programming - Basics main.c #incl
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C Programming - Basics default: pri
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C Programming - Basics struct tnode
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Unix Tools 4. UNIX TOOLS Tools of t
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Unix Tools Korn shell ! .profile HI
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Unix Tools grep "$name" $PHONEBOOK
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Unix Tools awk '$3 > 0 { print $1,
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Unix Tools END { print max, maxline
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Unix Tools Let an example input fil
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Unix Tools Brown eqn 1 # output Jon
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Development Tools Make looks at the
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Development Tools /* compute size o
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Development Tools #endif #line cons
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Development Tools 1.1 5 lines Retri
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Development Tools In Emacs, you may
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Development Tools */ %{ #define YYS
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C Libraries 6. C LIBRARIES Input an
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C Libraries } while (!feof(fp1)) pu
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C Libraries } free(p); /* what is w
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C Libraries } if ((fp->flag&( _READ
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C Libraries /* dirwalk: apply fcn t
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C Libraries } switch (pid=fork()){
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C Libraries What is curses? - libra
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C Libraries } if ((fd=fopen(argv[1]
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Introduction to kernel 7. INTRODUCT
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82 Introduction to kernel Programs
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Introduction to kernel } { printf("
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Introduction to kernel The kernel r
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Introduction to kernel UNIX Interna
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Introduction to kernel File System
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Introduction to kernel Every proces
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Processes I Process States 1. Execu
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Processes I } printf("%d %s\n", cnt
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Processes I dup (and other similar
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Processes I The u area contains - p
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Processes I The Context of a Proces
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Processes I Process Control use and
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Processes I Although the processes
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Processes I Handling Signals - proc
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Processes I USER=neville PATH=/user
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Processes I ! Shadow Password /etc/
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struct timeval { long tv_sec; /* se
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Processes I F_SETFL set status flag
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Processes I process is the child pr
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Processes I Rules about sharing of
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Processes II 9. PROCESSES (II) FORK
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Processes II /* background.c */ #in
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Processes II } while (1){ printf("p
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Processes II } /* child */ signal (
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Processes II int readline(int fd, c
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Processes II { } char process_name[
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Processes II - Pipe in a single pro
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Processes II System V IPC - message
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Processes II int msgctl(int msqid,
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Processes II For every semop operat
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Processes II /* client loop */ mesg
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I/O Subsystem Drivers frequently sl
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I/O Subsystem Terminal Drivers - In
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Working with the Unix OS

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