Basic Linux commands for DBAs - Part II

Permissions Related

Command	Description And Example
chmod	With help of this we can change the file permissions of a file, which can be assigned permissions to user, group and others 4 - (read), 2 - (write) and 1 - (execute). chmod 777 filename -- read, write and execute for all chmod 755 filename --rwx for owner, rw for group and others. -rwxrw-rw- First "-" indicates it’s a normal file if first character is "d" then it is a directory, first set or rwx (read, write and execute) belongs to owner, and second set of rwx belongs to group and third set of rwx belongs to others.
chown	Helps to change the owner and group of the file $ chown filename $ chown kalyan file1 -- It changes the owner of file to kalyan login How to change the owner and group $ chown :[groupname] filename $ chown kalyan:users file1 -- It changes the owner as "kalyan" and group as "users" for file1 How to change owner to all files in any folder $ chown -R $ chown -R Kalyan:Users /usr2/kalyan/jpgs
chgrp	Helps to change the group of the file, The difference between chown and chgrp is, using chown you can change the owner and group of a file, but using chgrp you can change on the group of the file not the owner $ chgrp filename $ chgrp bin /usr2/kalyan/myfile -- It changes the group of myfile to bin $ chgrp -R bin /usr2/kalyan/executables/ - It changes the group to bin for all files in the given path

Disk Space Related

Command	Description And Example
df	The df command stands for "disk filesystem", It displays how much space is occupied and how much space is available on file systems not directories and files $ df -- Displays file systems usage statistics when you run without any argument $ df -h -- Displays in human readable format $ df -h test -- It displays usage information of the filesystem where test resides, it wont give you size of test directory. -i- -- Displays inode information instead of block usage $ df -i. -- Displays inode information instead of block usage Switches -a -- Shows all file system disk usage -k -- Displays output in Kilobytes -i- --Displays inode information -t --Displays disk space usage for each of the specified type of file system -T --Displays file system type
du	The du command stands for "disk usage", this command will display usage information of a directory and sub-directory and displays the blocks that are occupied. Switches -a -- Write counts for all files, not just directories -h -- Displays output in human readable format -c -- To get the total usage in the output -s -- To get only total size in form of summary $ du -h -- Displays usage information of the given directory $ du -sh --Displays only size of the directory (nothing else will be printed) $ du -ahc --Displays all files human readable format including total size of the folder $ du -sh --exclude="*.txt" --Exclude the .txt files and provides the size of remaining all files