Unix For Testers
Unix System Architecture
Unix File System Structure
Absolute and Relative Path
Basic Unix Commands
cal command in Unix
who command in Unix
date command in Unix
clear command in Unix
more command in Unix
whoami command in Unix
uname command in Unix
man command in Unix
echo command in Unix
Unix File System Commands
ls command in Unix
cat command in Unix
cp command in Unix
mv command in Unix
pwd command in Unix
cd command in Unix
mkdir command in Unix
rmdir command in Unix
rm command in Unix
touch command in Unix
dirname command in Unix
tar command in Unix
Unix Links(ln)
Hard Link
Soft Link
Regular Expressions
Basic Regular Expressions
Interval Regular Expressions
Pipes and Filters
Unix Text Processing Commands
cmp command in Unix
diff command in Unix
comm command in Unix
cut command in Unix
Paste command in Unix
head command in Unix
tail command in Unix
wc command in Unix
sort command in Unix
grep command in Unix
Process Related Command
top command in Unix
ps command in Unix
nice command in Unix
Kill command in Unix
nohup command in Unix
time command in Unix
File Tranfer Commands in Unix
file transfer using scp command
file transfer using rlogin command
file transfer using telnet command
ssh(Secure Shell) command in Unix
ftp file transfer command
sftp file transfer command
chmod command in Unix
File Permission and File Security in Unix
Setting permission and changing ownership (chmod, chown)
File permissions are determined by who owns the file and the visibility of that file. chown and chmod are the tools we use to manipulate ownership and access. chown is used to change the owner, not the group.
chmod
The chmod command stands for “change mode”, and allows changing permissions of files and folders, also known as “modes” in UNIX.
- Used for setting file and directory permissions.
Syntax:
Chmod [OPTION] [Mode][Mode].. Filename
Using Absolute Mode:
chmod [0-7][0-7][0-7] filename/dir
Using Symbolic Mode:
chmod [ugo][+-=][rwx] filename
where + adds specified mode
– removes specified mode
= assigns specified mode for u/g/o
Option | Use |
-R | To change the file and directory permissions recursively |
–reference | Utilize permissions of first argument as reference to set permissions of remaining arguments |
Example:
- Chmod -R 755 /home/Data/task1
ls -l /home/Data/task1
Output:
drwxr-xr-x
umask
New files are created with a default set of permissions. Specifically, a new file’s permissions may be restricted in a specific way by applying a permissions “mask” called the umask. The umask command is used to set this mask, or to show you its current value.
- Stands for user creation mask.
- Sets default permissions for a newly created file and directory.
- Default value is 022.
- The value can be changed.
Syntax:
unmask
chown
The chown command stands for “change owner”, and allows changing the owner of a given file or folder, which can be a user and a group.
- Changing ownership for a file.
- Can be done only by the owner and root or administrator.
Syntax :
To change owner of the file:
chown username filename