Compression on a file works by:
Removing redundant information
Eliminating gaps within the file
Storing most of the data on removable media and just leaving a pointer
Consolidating multiple files into one
Removing the high order bit from each byte
In general, for which of the following would you want to use lossless compression?
A log file
A movie
A JPEG image
An mp3 audio file
An encrypted email
Lossy compression:
Decompresses to an identical version as the original
Is often used with documents
Is often used with images
Usually results better compression than lossless
Sacrifices some quality
You type gzip myfile.tar. What happens?
myfile.tar is removed
myfile.tar.gz holds a compressed version of myfile.tar
An error; you forgot to specify the file with –f
myfile.tar is unarchived into the current directory
An error; you forgot to pass the name of the output file
How would you obtain output similar to the following? compressed uncompressed ratio uncompressed_name 278168 1016950 72.6% tags
gunzip –t tags
file tags
gzip –l tags
Which command would you use to archive the Documents directory and compress it with bzip2 compression?
tar –czf documents.tbz Documents
tar –cjf Documents
tar –fzc Documents documents.tbz
tar –cjf documents.tbz Documents
tar –cf Documents documents.tbz
Which flag would you pass to tar in order to have it make a new archive?
–t
-c
–j
-x
–n
Which command will show what is inside the compressed tarball with a name of foo.tar.gz?
tar –tjf foo.tar.gz
tar –tzf foo.tar.gz
tar –lf foo.tar.gz
tar –xf foo.tar.gz
tar –tf foo.tar.gz
In the command tar –cvjf foo.tbz a b c, what are a, b, and c?
File names to be added to the archive
Matching operators; anything starting with a, b, or c will be added
a is the directory that will be prepended to files; b and c are files inside it
Extra flags passed to tar
Nothing; -cvjf only expects one parameter
Given the command tar –cvjf homedirs.tbz /home, which of the following are true?
The /home directory will be restored with the contents of homedirs.tbz
Only files starting with /home will be extracted from the archive
The command will print out each filename as it is processed
Files that are present in the archive might overwrite files in /home
The output file will be compressed
You archived your users’ directories into a file called backup.tar.gz. You then view the archive and see the filenames follow this convention: home/username/somefile
How will you extract just the files for the user called fred?
tar –tzf /home/fred < backup.tar.gz
tar –tjf backup.tar.gz /home/fred
tar –xjf backup.tar.gz home/fred/
tar –xzf backup.tar.gz home/fred/
tar –xzf backup.tar.gz fred
Which of the following commands will create a zipfile with the contents of your Documents directory?
zip –cf mydocs.zip Documents
zip –c mydocs.zip Documents
zip -r mydocs.zip Documents
zip mydocs.zip Documents
zip –f mydocs.zip Documents
Given a file called documents.zip, how can you see what’s in it without extracting the files?
showzip documents.zip
zip –lf documents.zip
zip –l documents.zip
unzip –list documents.zip
unzip –l documents.zip
Given a file called documents.zip, how can you extract just the files under ProjectX?
zip –x documents.zip ProjectX
unzip documents.zip | grep ProjectX
unzip –t documents.zip ProjectX
unzip documents.zip ProjectX
unzip documents.zip ProjectX/*
You try to compress a file that is already compressed. Which of the following statements is true?
The file will not be compressed any further than it already was
The compression algorithm needs to be set to the “currently compressed” mode for it to be compressed further
The file will actually be uncompressed
The file changed while you were compressing it
The file will be deleted
Which of the following commands can be used to compress a file?
bunzip2
bzip2
gzip
zip
cat
The three main modes of tar are:
Copy
List
Compress
Extract
Create
In the command tar –czf foo.tar.gz bar, what is the purpose of the f flag?
Tells tar to read from the file that follows the flag
Tells tar to print the name of each file as it is processed
Tells tar to copy only files, and not directories
Specifies extra compression is to be used
Tells tar to write to the file that follows the flag
Which two commands do the same thing?
tar –czf foo.tar.gz foo
tar –c foo | gzip > foo.tar.gz
tar –xzf foo.tar.gz
tar –x foo | gzip
The updatedb search locate find( updatedb, search, locate, find ) command is normally executed daily to update the database of all files that are on the system.
