APPLIED INFORMATICS Processes. Bash characteristics. Command type. Aliases.

Transcription

1 Lab 3 APPLIED INFORMATICS Processes. Bash characteristics. Command type. Aliases.

2 Today... /proc /run 1. PROCESSES 2. BASH CHARACTERISTICS 3. COMMAND TYPES 4. ALIASES $$ $PPID pidof ps pgrep kill killall pkill ps -C ps ax /proc/cpuinfo sleep top /run 2

3 FILE SYSTEM HIERARCHY 3

4 FILE SYSTEM HIERARCHY 4

5 /proc a means of interaction with the kernel cata@debian:~$ ls /proc 5

6 /proc files in /proc are continuously updated date ls al /proc after a while: cata@debian:~$ ls al /proc 6

7 /proc size 0 is displayed for lots of non-empty files in /proc cata@debian:~$ ls al /proc/cpuinfo cata@debian:~$ file /proc/cpuinfo cata@debian:~$ cat /proc/cpuinfo 7

8 /proc most files in /proc are read-only some ask for root permission some can be overwritten lots of files in /proc/sys can be overwritten 8

9 PROCESSES 9

10 Terms process: compiled source code running in the system PID: process ID (identifier) Each process has an ID. PPID: parent process ID Each process has a parent process. 10

11 init PID = 1 does not have a parent is started by the kernel is adoptive parent for all orphan processes 11

12 kill when the execution of a process is ended, it dies a process can be killed with the command kill 12

13 daemon processes being launched at start up run in background daemons never die 13

14 zombie when a process is killed and still appears as running in the system, then that process becomes a zombie. a zombie cannot be killed because it is already dead. 14

15 COMMANDS FOR PROCESSES 15

16 $$ & $PPID echo $$ returns the ID of the process associated to the bash echo $$ echo $PPID returns the ID of the parent process of the process associated to the bash echo $PPID echo $$ $PPID 16

17 pidof pidof process_name returns the ID of the process specified by its name pidof iceweasel pidof init 17

18 The relationship parent/child echo $$ $PPID bash echo $$ $PPID bash echo $$ $PPID ps exit ps exit 18

19 ps ps displays the processes associated to the bash ps ax displays all the processes in the system ps C process_name displays details of a specified process 19

20 pstree displays the processes in the system under the form of a tree cata@debian:~$ pstree 20

21 pgrep pgrep process_name returns the process ID for all the processes containing the specified name pgrep gnome 21

22 grep ps ax grep gnome returns all the processes in the system containing gnome in their name 22

23 top returns all the processes in the system under the form of a list cata@debian:~$ top Press h (help) for help. You can sort the list according to various criteriae. 23

24 Starting a process processes can be started from the terminal: cata@debian:~$ iceweasel Troubles? cata@debian:~$ iceweasel & starts the process in the background (so the bash becomes active) 24

25 Starting a process cata@debian:~$ sleep 10s cata@debian:~$ sleep 10s & cata@debian:~$ ps ax cata@debian:~$ ps -C sleep cata@debian:~$ sleep 1000 &... 25

26 kill kill process_id comand used for stopping a process cata@debian:~$ kill

27 Signals for kill kill l (the letter l, not the digit 1!) cata@debian:~$ kill -l 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP 21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ 26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR 31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3 38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8 43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13 48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7 58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2 63) SIGRTMAX-1 64) SIGRTMAX 27

28 kill -1 (SIGHUP) kill -1 process_id signal used to force a process to re-read its configuration file 1) SIGHUP cata@debian:~$ kill -1 1 Similarly: kill -HUP process_name 28

29 kill -15 (SIGTERM) kill -15 process_id command used to stop a process 15) SIGTERM cata@debian:~$ kill cata@debian:~$ kill

30 kill -19 (SIGSTOP) kill -19 process_id suspends a process 19) SIGSTOP cata@debian:~$ kill

31 kill -18 (SIGCONT) kill -18 process_id resumes a suspended process 18) SIGCONT cata@debian:~$ kill

32 pkill/killall pkill process_name kills a process by its name (not process_id) cata@debian:~$ pkill iceweasel cata@debian:~$ kill 2242 cata@debian:~$ killall iceweasel 32

33 top You can also kill processes from the top list. top Press k key to kill a process. Type in the process ID. Confirm the deletion. 33

34 BASH CHARACTERISTICS 34

35 Remember... echo displays the input received from the keyboard basic command in this lab: important command! Try: It is snowing outside! 35

36 Remember... Bash: Bourne Again Shell command interface used in the most Linux systems command interpreter in this lab: bash characteristics 36

37 Bash characteristics a command we type in the terminal is processed (and modified) by the bash, then executed first step: the bash scans the command then: divides the commands in arguments to be modified 37

38 Arguments each piece of text separated by one or several spaces or by tab, is considered an argument the command is an argument too Argument 3 Argument 5 cata@debian:~$echo It is Argument 1 Argument 2 Argument 4 (the command) Separator 2 Separator 1 (1 tab) (1 space) snowing outside! Separator 3 (2x space) 38

39 Arguments echo returns the arguments separated by a single space, no matter what the separator is Try: cata@debian:~$echo It is snowing outside! cata@debian:~$echo It is snowing outside! cata@debian:~$echo It is snowing outside! cata@debian:~$ echo It is snowing outside! 39

40 echo & by using you can avoid deletion of extra spaces and tabs Try: It is(tab)snowing outside! (2xspace)It is snowing outside! 40

41 echo & by using you can avoid deletion of extra spaces and tabs Try: It is(tab)snowing outside! (2xspace)It is snowing outside! 41

42 echo e & / with e option, or, /n and /t you can insert new lines or tabs in the text you want to display Try: cata@debian:~$echo -e A line with \na newline cata@debian:~$echo -e A line with \na newline cata@debian:~$echo -e A line with \ta tab cata@debian:~$echo -e A line with \ta tab 42

43 COMMAND TYPE 43

44 Command type 1) External commands having their own binary file saved locally on the computer (most can be found in bin and in sbin) 2) Internal (builtin) commands are integrated in the shell 44

45 type returns the command type Try: cd cat 45

46 type some commands are both internal and external internal type has priority in order to execute an external command the path to the binary file must be specified a echo 46

47 which displays the path to the binary folder corresponding to an external command cp ls cd mkdir pwd 47

48 ALIASES 48

49 alias the shell enables the creation of aliases for commands aliases are created with the purpose of replacing a difficult to recall command name with an easy name Create the file count.txt in which you write: 1, 2, 3 on three different lines. Then, try: cata@debian:~$alias reversed=tac cata@debian:~$reversed count.txt 49

50 alias aliases can be created in order to substitute complex commands md= mkdir p ~/D1/D2/ D3/D4 50

51 alias in order to list all the existing aliases in the computer : cata@debian:~$alias Try: cata@debian:~$alias invers md cata@debian:~$which md 51

52 unalias in order to deallocate an alias: reversed 52

53 That s all for today catalina.mancas@dcti.ucv.ro