linux notes ch3 file in file out

Creating  a file size  1Mb

$ dd if=/dev/zero of=junk.data bs=1M count=1
1+0 records in
1+0 records out
1048576 bytes (1.0 MB) copied, 0.00767266 s, 137 MB/s



intersection and set differances  (A-B)  on text files

commands : sort  comm

$ comm A.txt B.txt -1 -3
-2 -3 removes the second and third columns

finding and deleting dublicate files  

by comparing files content example script exist in pdf or web  awk {}  used



working with file permission, ownership and the stiky bit

chmod   used to modify the permission

chown used to change the ownership of the file

-R option to apply cmd recursively

The sticky bit is an interesting type of permission applied to directories. By setting the sticky
bit, it restricts only the user owning it to delete the files even though group and others may
have sufficient permissions.
In order to set the sticky bit, +t is applied on a directory with chmod as follows:
$ chmod a+t directory_name



Making File immutable

when a file is immutable  that means any user cannot remove it

/etc/mtab

immutable a way of securing the file such as  /etc/resolv.conf

command :  # chattr +i file or -i 



Using loopback files

command : mount -o loop, dd,

$ dd  if=/dev/zero of=muslum21.img  bs=1G count=1
$mkfs.ext4 muslum21.img 
$file muslum21.img  ##  to test file information approval

then mount to any folder create a folder mkdir   muslum_folder
$ mount -o loop muslum21.img  muslum_folder

now your storage is ready.



Creating iso files and hybrid iso

# cat /dev/cdrom > image.iso  or  # dd if=/dev/cdrom of=image.iso

$ mkisofs -V "Label" -o image.iso source_dir/

hybrid iso is for usb storage devices   with  command  isohybrid  it can be



Finding differences between files and patching 

command: diff, diff -u,

patch  -naur  for applying patches.



head and tail command :  first 10 lines and last 10 lines .

You will probably want to use this on logfiles. The command to monitor the growth of the files
would be:
# tail -f /var/log/messages