Hello there, this is the second week of my mastering Linux…

Linux Filesystem & Permissions

The Filesystem Hierarchy Standard (FHS) is commonly followed by Linux. It is made up of several branching subdirectories and one primary (or root) directory.

Root Directory ( / )

• The root directory / is the starting point for the entire Linux filesystem hierarchical tree.

• The root directory is owned by the root user (admin).

  Permissions :

  Permissions in Linux are as follows : (Owner-Group-Others)

• Elevating Privileges (sudo)

  The Linux shell has the sudo command that can temporarily elevate privileges to a user who is a member of the administrator group.

Linux Paths

• . - the current working directory

• .. - the parent directory

• ~ - the user's home directory

• cd - changing the current directory to user's home directory

• cd ~ - changing the current directory to user's home directory

• cd - - changing the current directory to the last directory

Installing tree

shows directories recursively in tree form

sudo apt install tree

tree directory/ Eg:

• tree -d > prints only directories

• tree -f > prints absolute paths

ls Command in detail :

• ls > listing the current directory

• ls -l > long listing

• ls -a > listing all files and directories including hidden ones

• ls -ld > displaying information about the directory, not about its contents

• ls -h > displaying the size in human readable format

• ls -Sh > displaying sorting by size

• du -sh > display the size of a directory and all its contents

• ls -lX > displaying sorting by extension

• ls --hide > hiding some files

  • ls --hide=*.log /var/log

• ls -lR > displaying a directory recursively

File Timestamps

• ls -lu > The access timestamp or atime is the last time the file was read (ls -lu)

• ls -l > The modified timestamp or mtime is the last time the contents of the file were modified (ls -l, ls -lt)

• ls -lc > The changed timestamp ctime is the last time when some metadata related to the file was changed (ls -lc)

Viewing files (cat, less, more, head, tail, watch):

viewing a file using cat

• cat filename > displaying the contents of a file

• cat -n filename > displaying the line numbers

• cat filename1 filename2 > filename3 > concatenating 2 files in a new file

viewing a file using less

• less filename > displays the content page by page

  • h > help

  • q > quit

  • enter > next line

  • space > next page

  • /string > search

  • ?string > search backwards

  • n / N > next/previous appearance

  • g / G > first page / last page

• tail filename > showing the last 10 lines of a file

• tail -n 15 filename > showing the last 15 lines of a file

• tail -n +5 filename > showing the last lines of a file starting with line no. 5

• tail -f filename > showing the last 10 lines of the file in real-time

• head filename > showing the first 10 lines of a file

• head -n 15 filename > showing the first 15 lines of a file

• watch -n 3 ls -l > running repeatedly a command with refresh of 3 seconds

Working with files and directory (touch, mkdir, cp, mv, rm, shred):

• mkdir dir1 > creating a new directory

• mkdir -p mydir1/mydir2/mydir3 > creating a directory and its parents as well

• cp file1 dir1/file2 > copying file1 to dir1 as another name (file2)

• cp -i file1 file2 > copying a file prompting the user if it overwrites the destination

• cp -p file1 file2 > preserving the file permissions, group and ownership when copying

• cp -r dir1 dir2/ > recursively copying dir1 to dir2 in the current directory

• mv file1 file2 > renaming file1 to file2

• mv file1 dir1/ > moving file1 to dir1

• mv -i file1 dir1/ > moving a file prompting the user if it overwrites the destination file

• mv -n file1 dir1/ > preventing a existing file from being overwritten

• mv -u file1 dir1/ > moving only if the source file is newer than the destination file or when the destination file is missing

• mv file1 dir1/file2 > moving file1 to dir1 as file2

• mv file1 file2 dir1/ dir2/ destination_directory/ > moving more source files and directories to a destination directory

• rm file1 > removing a file

• rm -r dir1/ > removing a directory

• rm -rf dir1/ > removing a directory without prompting

• rm -ri fil1 dir1/ > removing a file and a directory prompting the user for confirmation

• shred -vu -n 100 file1 > secure removal of a file (verbose with 100 rounds of overwriting)

Piping and Command Redirection:

Using the pipe symbol (|) we can connect two or more commands at a time.

command1 | command2 | command3 ….

Finding Files (find, locate)

• sudo updatedb > updating the locate db

• locate -S > displaying statistics

• locate filename > filename is expanded to filename

• locate -i filename > the filename is case insensitive

• locate -b '\\filename' > finding by exact name

• locate -b filename > finding using the basename

• locate -r 'regex' > finding using regular expressions

• locate -e filename > checking that the file exists

• which command > showing command path

• which -a command

FIND

• find PATH OPTIONS

Example: find ~ -type f -size +1M # => finding all files in ~ bigger than 1 MB

Options:

• -type f, d, l, s, p

• -name filename

• -iname filename # => case-insensitive

• -size n, +n, -n

• -perm permissions

• -links n, +n, -n

• -atime n, -mtime n, ctime n

• -user owner

• -group group_owner

Will learn the other commands in the following week (there are lots to learn🧐).

./See you next week…