UNIX Destillate

• This is an extremely short quick introduction to UNIX.
• This introduction assumes you know how to use computers and how to adopt the examples for your needs.
• Further, this introduction assumes you are familiar with operating systems in general.

Basics

• Everything [in UNIX] is a file.
• There are regular files, directories, pipes, sockets, devices, soft links and more kinds of files.
• A directory can contain many files of different kinds.

Concepts

Permissions

Every file object has 12 bits for permissions:

• The special bits SetUID (4), SetGID (2), Sticky (1)
• Read (4), Write (2), Execute (1) each for the user that owns the file, the associated group and others

Binary Permission Notation

Symbolic Permission Notation

• u Owning User
• g Associated Group
• o Others
• a All (Explicit, ignoring umask)
• All (Implicit, respecting umask)

• r Read
• w Write
• x Execute
• s SetUID / SetGID
• t Sticky

Examples: a=rwx u=rw u+s

Permission Notation of ls

The output of ls shows special bits and executable bits in the same column.

• SetUID: user
• SetGID: group
• Sticky: other

The UMASK

The UMASK is a process-bound property with a permission mask for newly created files. The bits that are set in UMASK will be deleted from the permissions of a newly created file. (NAND). Files are created with 0666, directories with 0777 permission.

Commands

File Commands

Create / update a file

touch file

Copy a file

cp name nameOfCopy
cp name destinationDirectory

Rename or move a file

mv oldName newName
mv name destinationDirectory
If used within the same filesystem, the mv command only changes the hardlink.

Delete a file

rm name
This command only removes one hardlink ("unlink"). A file (including its inode) is only freed by the removal of its very last hardlink.

Show a regular file's contents

• cat name
• more name
• less name
• view name

Copying data from a file (also devices)

dd if=infile of=outfile

Concatenating files

cat files...

Delete contents of files

shred files...

Commands for Directories

Create a directory

mkdir dirName

Show a directory's contents

Current directory: ls
Specified directory: ls dirName
Show hidden files: ls -a
Detailed listing: ls -l
Show a directory itself, not its content: ls -d

Print working directory

pwd

Change working directory

cd dirName
Parent directory: cd ..
Root directory: cd /
Home directory: cd ~ oder einfach nur cd

Delete a directory

rmdir dirName (Directory must be empty)
rm -r dirName (deletes with content, Caution!)

Permissions

Change owner

chown newOwner files

Change group

Of a file: chgrp newGroup files
Of the current user: newgrp newGroup

Change file permissions

chmod bits files

Extended Permissions (ACLs)

Activating ACLs

mount -o remount,acl mountpoint

Giving a user additional permissions

setfacl -m user:username:permissionsfiles...

Giving a group additional permissions

setfacl -m group:groupname:permissionsfiles...

Creating a Default-ACL for newly created files

setfacl -m default:user|group:userorgroupname:permissionsdirs...

Modifying the permission mask

setfacl -m mask::permissions

Processes and Job-Control

End a process

• Process with tty: Ctrl-C drücken
• kill processNumber
• Process doesn't respond: kill -9 processNumber

List processes

Own / Subshells: ps
Jobs of current shell: jobs
All: ps -aef

Start process as background job

cmd &

Suspend current process / job

Ctrl-Z

Resume suspended process

fg

Continue process in background

1. Ctrl-Z
2. bg

Suspend STDIN

Ctrl-S

Resume STDIN

Ctrl-Q

Send EOF to STDIN

Ctrl-D

STDOUT, STDIN and Pipes

Redirection

STDIN: cmd <name
STDOUT: cmd >name
STDERR: cmd 2>name
STDOUT a. STDERR to the same file: cmd >name 2>&1

Use a command's output as input for a second command

cmd1 | cmd2

Use a file as a command's input

• cat name | cmd
• cmd <name

Use a command's output as arguments for a second command

Some arguments: cmd2 `cmd1`
Many arguments: cmd1 | xargs cmd2

Send EOF to STDIN

Ctrl-D

Commands for archives and compressed files

gzip

Compress: gzip name Decompress: ungzip name

bzip2

Compress: bzip2 name Decompress: bunzip2 name

tar-archives

Create: tar cvf archiveName.tar dir
List contents: tar tvf archiveName.tar
Extract: tar xvf archiveName.tar
Automatically invoke gzip using z: tar czvf / tzvf / xzvf
Automatically invoke bzip2 using j: tar cjvf / tjvf / xjvf

jar-archives

Like tar-archives, options j and z do not apply.

Burn CDs

Burn a directory on CD

1. mkisofs -R -J -o /tmp/image.iso dir
2. cdrecord speed=16 dev=0,1,0 /tmp/image.iso
3. rm /tmp/image.iso

Burn a directory on CD-RW

1. mkisofs -R -J -o /tmp/image.iso dir
2. cdrecord speed=16 dev=0,1,0 blank=all /tmp/image.iso
3. rm /tmp/image.iso

Test iso-image before burning

1. mkdir /tmp/image
2. mount -o loop -t iso9660 /tmp/image.iso /tmp/image
3. ls /tmp/image
4. umount /tmp/image
5. rmdir /tmp/image