Other Tools

ssh

ssh command is used to connect to a remote machine using Secure Shell Protocol (default port is 22)

# generate asymmetric key pair (default is RSA)
$ ssh-keygen

$ ssh user@server

# specify a diff port
$ ssh root@192.168.1.5 -p 998

# run a command on remote server
$ ssh root@192.168.1.5 'ls -la'

scp (Secure Copy) command is used to transfer files to-and-fro between the server and client.

Compression and Archival

Zipping

gzip creates compressed file with .gz extension. It can only compress a single file or directory at a time.

$ gzip myfile 

# recursive; use on directories
$ gzip -r mydir

# decompress
$ gzip -d myfile.gz
$ gunzip myfile.gz

Upon compression, the file is moved to the compressed file (.gz). And on uncompression, the comressed (.gz) file is deleted.

Other tools like bzip2 and xz can also be used. They are not recursive though so they can’t compress directories unlike gzip.

Looking inside

gzcat, bzcat, xzcat, zcat

Used to print compressed file’s content onto the terminal without uncompressing them.

Archiving

tar cpio

We can put multiple files in a single one (called “archive”).

# create tarball 
$ tar -cf myfile.tar foofile barfile

# extract tarball
$ tar -xf myfile.tar

# filter (compress/uncompress) with gzip, bzip upon achival/unarchival automatically
-z -b

# show archive content
-t

# show extracted content names in terminal
-v 

# add files to existing archive
-r

The order of parameters matter in the tar command, better skip the hyphen (-) when specifying them, then order doesn’t matter at all.

$ tar -cfzv foobar.tar foo.txt bar.txt		# error!
$ tar cfzv foobar.tar foo.txt bar.txt

Reference: https://unix.stackexchange.com/questions/239118/does-parameter-order-matter-with-tar

tar can work with tapes and drives too, so we need to specify that we’re archiving files or directories using the -f flag. So this goes everytime we use this command under normal circumstances.

It doesn’t remove the original file or archive upon archival or extraction respectively, unlike compression (gzip, bzip2, xz) tools above.

Hashing

md5sum sha256sum sha512sum

# generate MD5 hash and write to a file
$ md5sum foo.txt > mysumfile

# check hash from generated file against file
$ md5sum -c mysumfile

$ cat mysumfile
63a684f882686068b5182c7eab91d359c180cfa644daf64977725c6857ee4aaa *foo.txt