Red Hat Certification

Stuff to review:

• Manage Networking
• Install & Update Software
  • create repos
• Improve command line productivity
• Schedule future tasks
• Tune System Performance
• Controlling access to files with ACL
• Managing SELinux Security

Side Notes:

• ls -ltr
  • List all files with full details, the time, and in reverse order
• df
  • List file systems
• du
  • Disk usage
• df/du -h
  • Make human-readable
• wc -l
  • Word Count with -l meaning count lines
• rpm -qa
  • -q means query
  • -a means all
  • List all packages installed
• rpm -ihv /location/of/file/here
  • Install a rpm package
• rpm -e packageName
  • Remove a package
• rpm -qi
  • Information about the package
• rpm -qc
  • List config files for that package
• rpm -qf /binary/file/here
  • Get associated package name from binary
• which commandNameHere
  • Get command’s binary file location

• Bash Scripting

  • All scripts start with:
    • #!/bin/bash
  • echo outputs what is in front of it.
  • If statements are structured like so:

  #!/bin/bash
   
  count=100
  # -eq stands for Equals
  if [ $count -eq 100 ]
  then
  	echo Count is 100
  else
  	echo Count is not 100
  fi

  Or

  #!/bin/bash
  clear
  # -e stands for if a file exists
  # -x if file exists AND is executable
  if [ -e /home/lucky/error.txt]
  	then
  	echo "File exist"
  	else
  	echo "File does not exist"
  fi

  • Loops are structured like so:

  #!/bin/bash
  for i in 1 2 3 4 5
  do
  echo "Welcome $i times"
  done

  Or

  #!/bin/bash
   
  for i in dog jeff bob
  do
  echo $i
  done

  Or

  #!/bin/bash
  # Numbers 1-5
  for i in {1..5}
  do
  echo Number $1
  done

  Link to original

• grep
  • global regular expression print
  • Basic search for given text
  • Flags
    • -c
      • Keyword count
    • -i
      • Ignore case-sensitive
    • -n
      • Give line numbers
    • -v
      • Everything except given search term
• awk
  • Used for dividing lines by spaces
  • Often used with grep
  • e.g.
    • awk '{print $1}'
      • Will output the first item in a line
    • awk '{print $1}'
      • Prints everything in the file (Essentially does cat)
  • Can change dividing points from spaces to something else by doing
    • awk -F ":" '{print $1}'
      • This converts from spaces to :
• cut
  • Used to cut off beginning or end of line
  • Also often used with grep
  • e.g.
    • cut -c1-3
      • Spits back only the first 3 characters
• egrep
  • Same as grep but allows for more than one keyword in order found in the file
  • e.g. egrep -i "keyword|keyword2" file
• crontab
  • Used to regularly schedule tasks
  • e.g.
    • crontab -e
      • Creates a crontab file that enables you to make a script for that cron
• tuned (pronounced tune-dee)
  • Used to tune Linux system performance
  • e.g.
• nice
  • Used to set user priority to certain tasks
  • e.g.
    • nice -n # process-name
• renice
  • Used to change active process priority
  • e.g.
    • renice -n # process-name
• setfacl -m u:lucky:rw /tmp/tx
  • Set user specific permission
• setfacl -b /tmp/tx
  • Resets permissions to just basic file permissions