Chapter 3 RHCSA Notes - File Management

7 File types

  1. regular
  2. directory
  3. block special device
  4. character special device
  5. symbolic link
  6. named pipe
  7. socket

Commands

  • ls
  • stat
  • file

Regular files

  • Text or binary data.
  • Represented by hyphen (-).

Directory Files

  • Identified by the letter “d” in the beginning of ls output.

Block and Character (raw) Special Device Files

  • All hardware has device file in /dev/.
  • Used by system to communicate with device.
  • Identified by “c” or “b” in ls listing.
  • Each device driver is assigned a unique number called the major number
  • Character device
    • reads and writes 8 bits at a time
    • Serial
  • Block device
    • Receives data in fixed block size determined by drivers
    • 512 or 4096 bytes

Major Number

  • Used by kernel to recognize device driver type.
  • Column 5 of ls listing.
ls -l /dev/sda

Minor Number

  • Each device controlled by the same device driver gets a Minor Number
  • Applies to disk partitions as well.
  • The same driver can control multiple devices of the same type.
  • Column 6 of ls listing
ls -l /dev/sda
  • Shortcut to another file or directory.
  • Begins with “l” in ls listing.
ls -l /usr/sbin/vigr
lrwxrwxrwx. 1 root root 4 Jul 21 14:36 /usr/sbin/vigr -> vipw

Compression and Archiving

Archiving

  • Preserves file attributes such as ownership, owning group, and timestamp.
  • Preserves extended file attributes such as ACLs and SELinux contexts.
  • Syntax of tar and star are identical.

star command

tar (tape archive) command

  • Create, append, update, list, and extract files/directory tree to/from a file called a tarball(tarfile)
  • Can compress a tarball after it’s been created.
  • Automatically removes “/” so you do not have to specify the full pathname  when restoring files at any location.

flags tar -c :: Create tarball. tar -f :: Specify tarball name. tar -p :: Preserve file permissions. Default for the root user. Specify this if you create an archive as a normal user. tar -r :: Append files to the end of an existing uncompressed tarball. tar -t :: List contents of a tarball. tar -u :: Append files to the end of an existing uncompressed tarball provided the specified files being added are newer. -z -j -C

Archive entire home directory:

tar -cvf /tmp/home.tar /home

Archive two specific files:

tar -cvf /tmp/files.tar /etc/passwd /etc/yum.conf

Append files in a directory to existing tarball:

tar -rvf /tmp/files.tar /etc/yum.repos.d

List what is included in home.tar tarball:

tar -tvf /tmp/files.tar

Restore single file and confirm:

tar -xf /tmp/files.tar etc/yum.conf
ls -l etc/yum.conf

Restore all files and confirm:

tar -xf /tmp/files.tar
ls

Create a gzip-compressed tarball under /tmp for /home:

tar -czf /tmp/home.tar.gz /home

Create bzip2-compressed tarball under /tmp for /home:

sudo tar -cjf /tmp/home.tar.bz2 /home

List content of gzip-compressed archive without uncompressing it:

tar -tf /tmp/home.tar.gz

Extract files from gzip-compressed tarball in the current directory:

tar -xf /tmp/home.tar.gz

Extract files from the bzip2-compressed tarball under /tmp:

tar -xf /tmp/home.tar.bz2 -C /tmp

Compression tools

gzip (gunzip) command

  • Create a compressed file for each of the specified files.
  • Adds .gz extension.

Flags

Copy /etc/fstab to the current directory and display filename when uncompressed:

cp /etc/fstab .
ls -l fstab

gzip fstab and view details:

gzip fstab
ls -l fstab.gz

Display compression info:

gzip -l fstab.gz

Uncompress fstab.gz:

gunzip fstab.gz
ls -l fstab

bzip2 (bunzip2) command

  • Adds .bz2 extension.
  • Better compression/ decompression ratio but is slower than gzip.

Compress fstab using bzip and view details:

bzip2 fstab
ls -l fstab.bz2

Unzip fstab.bz2 and view details:

bunzip2 fstab.bz2
ls -l fstab

File Editing

Vim

vimguide

File and Directory Operations

touch command

  • File is created with 0 bytes in size.
  • Run touch on it and it will get a new timestamp

Flags

Set date on file1 to 2019-09-20:

touch -d 2019-09-20 file1

Change modification time on file1 to current system time:

touch -m file1

mkdir command

  • Create a new directory.

flags

Create dir1 verbosely:

mkdir dir1 -v

Create dir2/perl/perl5:

mkdir -vp dir2/perl/perl5

Commands for displaying file contents

  • cat
  • more
  • less
  • head
  • tail

cat command

  • Concatenate and print files to standard output.

Flags

Redirect output to specified file:

cat > catfile1

tac command

  • Display file contents in reverse

command

  • Display files on page-by-page basis.
  • Forward text searching only.

less command

  • Display files on page-by-page basis.
  • Forward and backwards searching.
less /usr/bin/znew

head command

  • Displays first 10 lines of a file.
head /etc/profile

View top 3 lines of a file:

head -3 /etc/profile

tail command

  • Display last 10 lines of a file.

Flags

tail /etc/profile

View last 3 lines of /etc/profile:

tail -3 /etc/profile

View updates to the system log file /varlog/messages in real time:

sudo tail -f /var/log/messages

Counting Words, Lines, and Characters in Text Files

wc (word count) command

  • Display the number of lines, words, and characters (or bytes) contained in a text file or input supplied.

Flags

 wc /etc/profile
  85  294 2123 /etc/profile

Display count of characters on /etc/profile:

wc -m /etc/profile

Copying Files and Directories

cp command

  • Copy files or directories.
  • Overwrites destination without warning.
  • root has a custom alias in their .bashrc file that automatically adds the -i option.
alias cp='cp -i'

Flags

cp file1 newfile1

Copy file to new directory:

cp file1 dir1

Get confirmation before overwriting:

cp file1 dir1 -i
cp: overwrite 'dir1/file1'? y

Copy a directory and view hierarchy:

cp -r dir1 dir2
ls -l dir2 -R

Copy file while preserving attributes:

cp -p file1 /tmp

Moving and renaming Files and Directories

mv command

  • Move or rename files and directories.
  • Can move a directory into another directory.
    • Target directory must exist otherwise you are just renaming the directory.
  • Alias exists in root’s home directory for -i in the .bashrc file.
alias—“alias mv=’mv -i’""

Flags

mv -i file1 dir1
mv newfile1 newfile2

Move a dir into another dir (target exists):

mv dir1 dir2

Rename a directory (Target does not exist):

mv dir2 dir20

Removing files

rm command

  • Delete one or more specified files or directories.
  • Alias—“alias rm=’rm -i’”— in the .bashrc file in the root user’s home directory.
  • Remember to backslash “" any wildcard characters in filenames.

Flags

Erase newfile2:

rm -i newfile2

rm a directory:

 rm -dv emptydir

rm a directory recursively:

rm -r dir20

rmdir command

  • Remove empty directories.

Flags

rmdir emptydir -v

File Linking

inode (index node)

  • Contains metadata about a file (128 bytes)
    • File type, Size, permissions, owner name, owning group, access times, link count, etc.
    • Also shows number of allocated blocks and pointers to the data storage location.
  • Assigned a unique numeric identifier that is used by the kernel for accessing, tracking, and managing the file.
  • Does not store the filename.
  • Filename and corresponding inode number mapping is maintained in the directory’s metadata where the file resides.
  • Links are not created between files and directories
  • Mapping between one or more filenames and an inode number.
  • Hard-linked files are indistinguishable from one another.
  • All hard-linked files will have identical metadata.
  • Changes to the file metadata and content can be made by accessing any of the filenames.
  • Cannot cross file system boundaries.
  • Cannot link directories.

ls -li output

  • Column 1 inode number.
  • Column 3 link count.
  • Symbolic (symlink).
  • Like a Windows shortcut.
  • Unique inode number for each symlink.
  • Link count does not increase or decrease.
  • Size of soft link is the number of character in pathname to target.
  • Can cross file system boundaries.
  • Can link directories.
  • ls-l shows l at the beginning of the permissions for soft link
  • if you remove the original file, the softlink will point to a file that doesn’t exist.
  • RHEL 8 has four soft-linked directories under /.
    1. bin -> usr/bin
    2. lib -> usr/lib
    3. lib64 ->usr/lib64
    4. sbin -> usr/sbin
  • Same syntax for creating linked directories

ln command

  • Create links between files.
  • Creates hard link by default.
touch file10
ln file10 file20
ls -li
ln -s file10 soft10

Copying vs linking

Copying

  • Duplicates source file.
  • Each copy stores data at a unique location.
  • Each copied file has a unique inode number and unique metadata.
  • If a copy is moved, erased, or renamed, the source file will have no impact, and vice versa.
  • Copy is used when the data needs to be edited independent of the other.
  • Permissions on the source and the copy are managed independent of each other.

Linking

  • Creates a shortcut that points to the source file.
  • Source can be accessed or modified using either the source file or the link.
  • All linked files point to the same data.
  • Hard Link: All hard-linked files share the same inode number, and hence the metadata.
  • Symlink: Each symlinked file has a unique inode number, but the inode number stores only the pathname to the source.
  • Hard Link: If the hard link is weeded out, the other file and the data will remain untouched.
  • Symlink: If the source is deleted, the soft link will be broken and become meaningless. If the soft link is removed, the source will have no impact.
  • Links are used when access to the same source is required from multiple locations.
  • Permissions are managed on the source file.

Labs

Lab: Viewing regular file information:

touch file1
ls -l
file file1
stat file1
  1. Create an empty file /tmp/hard1, and display the long file listing including the inode number:
touch /tmp/hard1
ls -li /tmp/hard1
  1. Create two hard links called hard2 and hard3 under /tmp, and display the long listing:
ln /tmp/hard1 /tmp/hard2
ln /tmp/hard1 /tmp/hard3
ls -li /tmp/hard*
  1. Edit file hard2 and add some random text. Display the long listing for all three files again:
vim /tmp/hard2
ls -li /tmp/hard*
  1. Erase file hard1 and hard3, and display the long listing for the remaining file:
rm -f /tmp/hard1 /tmp/hard3
ls -li /tmp/hard*
  1. Create soft link /root/soft1 pointing to /tmp/hard2, and display the long file listing for both:
sudo ln -s /tmp/hard2 /root/soft1
ls -li /tmp/hard2 /root/soft1
sudo ls -li /tmp/hard2 /root/soft1

2.Edit soft1 and display the long listing again:

sudo vim /root/soft1
sudo ls -li /tmp/hard2 /root/soft1

3.Remove hard2 and display the long listing:

sudo ls -li /tmp/hard2 /root/soft1

remove the soft link

rm -f /root/soft1.

Lab: Archive, List, and Restore Files

Create a gzip-compressed archive of the /etc directory.

tar -czf etc.tar.gz /etc

Create a bzip2-compressed archive of the /etc directory.

sudo tar -cjf etc.tar.bz2 /etc

Compare the file sizes of the two archives.

ls -l etc*

Run the tar command and uncompress and restore both archives without specifying the compression tool used.

sudo tar -xf etc.tar.bz2 ; sudo tar -xf etc.tar.gz

Lab: Practice the vim Editor

As user1 on server1, create a file called vipractice in the home directory using vim. Type (do not copy and paste) each sentence from Lab 3-1 on a separate line (do not worry about line wrapping). Save the file and quit the editor.

Open vipractice in vim again and reveal line numbering. Copy lines 2 and 3 to the end of the file to make the total number of lines in the file to 6.

:set number!
#then
yy and p

Move line 3 to make it line 1.

3m0

Go to the last line and append the contents of the .bash_profile.

:r ~/.bashrc

Substitute all occurrences of the string “Profile” with “Pro File”, and all occurrences of the string “profile” with “pro file”.

:%s/profile/pro file/gi

Erase lines 5 to 8.

:5,8d

Provide a count of lines, words, and characters in the vipractice file using the wc command.

wc vipractice

Lab: File and Directory Operations

As user1 on server1, create one file and one directory in the home directory.

touch file3
mkdir dir5

List the file and directory and observe the permissions, ownership, and owning group.

ls -l file3
ls -l dir5
ls -ld dir5

Try to move the file and the directory to the /var/log directory and notice what happens.

mv dir5 /var/log
mv file3 /var/log

Try again to move them to the /tmp directory.

mv dir5 /tmp
ls /tmp

Duplicate the file with the cp command, and then rename the duplicated file using any name.

cp /tmp/file3 file4
ls /tmp
ls

Erase the file and directory created for this lab.

rm -d /tmp/dir5; rm file4