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Operating Systems

slide 13 updated April 28 th. Operating Systems. Recitation 5, April 21-22, 2002. Shell. Interactive use Session customization Programming. User. Linux shell program. Linux kernel. Command interpretation by the shell. user commands. Shell. Shell commands cd, pwd, kill, exit, etc.

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Operating Systems

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  1. slide 13 updated April 28th Operating Systems Recitation 5, April 21-22, 2002

  2. Shell • Interactive use • Session customization • Programming User Linux shell program Linux kernel

  3. Command interpretation by the shell user commands Shell Shell commands cd, pwd, kill, exit, etc. External commands Unix utility programs ls, rm, cp, etc. Other applications emacs, xv, etc. Unix kernel Unix system calls fork, iocntl, read, exec, open, write, etc.

  4. csh (C shell) - example 1 • A series of individual commands (shell or other Linux commands) combined into one executable file is called a shell script, similar to a batch file in MS-DOS. • Many of the programming constructs resemble those of C. #!/bin/csh foreach f (*) echo $f end ls -l [root@pc ex-ps]# csh ex-ls

  5. csh - example 2 #!/bin/csh set argc = $#argv if ($argc < 2) then echo "usage: ex-mv <extension> <filenames>" exit(1) endif set extension = $argv[1] set filenames = ($argv[2-$argc]) foreach name ($filenames) set prefix = $name:r set newname = $prefix.$extension mv $name $newname end [root@pc ex-ps]# csh ex-mv cpp 1.c 2.c

  6. csh - example 3 set column = 5 set sum = 0 foreach file ($filenames) set line = `ls -l $file` set filesize = $line[$column] if ($filesize > $size) then echo $file endif @ sum = $sum + $filesize end @ n = $argc - 1 if ($n != 0 && $sum != 0) then @ average = $sum / $n echo "average size is $average" endif #!/bin/csh set argc = $#argv if ($argc < 2) then echo "usage: ex-large <size> <filenames>" exit(1) endif set size = $argv[1] set filenames = ($argv[2-$argc]) …

  7. Virtual file system • Kernel software layer that handles system calls related to a standard Unix file-system. • Common model representing all supported file systems: disk-based, network, and special file-systems that do not manage disk space at all, such as the process file-system.

  8. Example cp ]# cp /floppy/TEST /tmp/test Virtual file system Ext2 MS-DOS /floppy/TEST /tmp/test

  9. Process file system (/proc) • Interface, no persistent data. • Each subdirectory corresponds to an active process, directory name is PID. • Additional directories provide global statistics about the kernel and drivers. • Access via plain text, computed on demand.

  10. Example [root@pc os]# emacs HelloWorld.java & [1] 2912 [root@pc os]# cd / [root@pc /]# cd proc [root@pc /proc]# ls 1 1292 1408 1972 4 8 cmdline interrupts meminfo slabinfo 1007 1296 1409 1974 5 845 cpuinfo … 2912 … [root@pc /proc]# cd 2912 [root@pc 2912]# ls -l total 0 -r--r--r-- 1 root root 0 Apr 20 01:18 cmdline lrwxrwxrwx 1 root root 0 Apr 20 01:18 cwd -> /home/idrori/os -r-------- 1 root root 0 Apr 20 01:18 environ lrwxrwxrwx 1 root root 0 Apr 20 01:18 exe -> /usr/bin/emacs dr-x------ 2 root root 0 Apr 20 01:18 fd -r--r--r-- 1 root root 0 Apr 20 01:18 maps -rw------- 1 root root 0 Apr 20 01:18 mem lrwxrwxrwx 1 root root 0 Apr 20 01:18 root -> / -r--r--r-- 1 root root 0 Apr 20 01:18 stat -r--r--r-- 1 root root 0 Apr 20 01:18 statm -r--r--r-- 1 root root 0 Apr 20 01:18 status

  11. Example [root@pc 2912]# more cmdline emacsHelloWorld.java [root@pc 2912]# more status Name: emacs State: S (sleeping) Pid: 2912 PPid: 2189 TracerPid: 0 Uid: 0 0 0 0 Gid: 0 0 0 0 FDSize: 32 Groups: 0 1 2 3 4 6 10 VmSize: 9000 kB … VmData: 896 kB VmStk: 672 kB VmExe: 992 kB VmLib: 3576 kB SigPnd: 0000000000000000 SigBlk: 0000000000000000 SigIgn: 8000000000000000 ... [root@pc 2912]#

  12. Exercise description • Write a csh program (ex-ps) that specifies the running processes in the system, their user name and running command. The program should print a line for each process.

  13. Exercise - notes • Write a small C program, isnum.c (whose executable is isnum), that checks if its argument is numeric, and use it to check for directories in proc that correspond to processes. • The following table provides the location of necessary information: • you can use the –x flag to echo each line of your script (for debugging purposes only) • #!/bin/csh -x

  14. Notes • When you log in, the system determines which shell to run by your entry in /etc/passwd • The default shell on Linux is bash. • You can change the shell using the command chsh –s /bin/csh , or by typing the program name at the command line, exec csh

  15. Chapter 4.10, pages 77-78, in Toledo’s book. • Submission: Monday, May 6th. • Software Directory: ~username/os02b/ex-ps Files: ex-ps, isnum.c Permissions: chmod ugo+rx (to above) • Hardcopy name, ID, login, CID ex-ps, isnum.c submit in mailbox 281, Nir Neumark, nirn@post.tau.ac.il

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