terminal or shell
Bash csh zsh ksh sh
commands are used to interact with the shell
ls - list directories and files
ls -l [long list format]
mkdir - make directories
cd - change directories
cd .. [one directory back]
cd / [go to root directory]
cd ~ [go to home directory]
pwd - present working directory
clear - clear the screan
cat - concatinate [view the contents of a file]
nano,vi,emacs - text editor
man - manual [helps to find the use of commands]
echo - print to the screen
tr - translate or delete chars
ctrl+d - to exit
whereis - location of command/bin
file - determine file type
history - list of command used
wc - [wordcount] prints the numbr of lines,words,chars/bytes
| - pipe symbol [pass output from one as input to another]
tee - read from standard input and write to standard output
chmod - change modification
r = read 4,
w = write 2,
x = execution 1
chmod -x [remove execution permission]
chmod +x [add execution permission]
Redirect
output redirect
> - redirect
>> - redirect[append to file/no rewrite]
input redirect
< - read from file
ps -process status
ps -el [long list format]
pstree - shows process in heirarchical structure
root - systemd,init
kthreadd - parent of all kernel
Sys calls
Functions for using kernel mode
fork() - to create a new process[new process- child process]
child process returns - 0
parent returns - +ve pid
error - -ve value
exec() - to execute binaries/executable files
execl("/usr/bin/ls","ls","-l",NULL) [execl is one form of exec]
The first parameter of each function denotes the pathname of the file to be executed.A variable number of additional parameters. Each points to a string describing a command-line argument for the new program.
getpid() - gets the process id[+ve if there is no error | not zero for child]
exit() - exit the process
wait() >>- blocks the calling process until one of its child processes exits or a signal is received. A zombie process or defunct process is a process that has completed execution but still has an entry in the process table
close() -
stat() - status/state
opendir() - open directory
readdir() - read contents of directories