Lesson 2: Single System Fundamentals¶

Or, how to be a power user.

Housekeeping¶

10 minutes to make sure everyone’s Virtualbox instances are up and running

Your opinions:

Want to meet during dead week vs. have last meeting of term next week?
Start wk1 of winter term?

Today’s Topics¶

What are files?
- Permissions/users
What are user accounts?
- User management
- Root vs. normal
- Groups
What are packages?
- How to use package managers
- Differences between Linux Distributions
- Other package managers

What are users?¶

You, right now

$ whoami    # your username
$ who       # who is logged in?
$ w         # who is here and what are they doing?
$ id        # user ID, group ID, and groups you're in

Not just people: Apache, Mailman, ntp

Users have¶

Username
UID
Group
Usually (but not always) password
Usually (but not always) home directory

Managing users¶

$ cat /etc/passwd
# username:x:UID:GID:GECOS:homedir:shell
$ useradd $USER # vs adduser, the friendly Ubuntu version
$ userdel $USER
$ passwd

# GECOS: full name, office number and building, office phone extension,
# home phone number (General Electric Comprehensive Operating System)
$ chfn # change GECOS information; only works sometimes
$ finger # tells you someone's GECOS info

Passwords¶

/etc/shadow, not /etc/passwd

test@x230 ~ $ ls -l /etc/ | grep shadow
-rw-r-----  1 root shadow   1503 Nov 12 17:37 shadow

$ sudo su -
$ cat /etc/shadow
daemon:*:15630:0:99999:7:::
bin:*:15630:0:99999:7:::
sys:*:15630:0:99999:7:::
mail:*:15630:0:99999:7:::

# name:hash:time last changed: min days between changes: max days
#    between changes:days to wait before expiry or disabling:day of
#    account expiry

$ chage # change when a user's password expires

Root/Superuser¶

UID 0
sudo

Acting as another user¶

$ su $USER          # become user, with THEIR password
$ su                # become root, with root's password
$ sudo su -         # use user password instead of root's
$ sudo su $USER     # become $USER with your password

If someone has permissions errors:

Check that they or their group owns the files
Check that they have the flag +x to execute

What are groups?¶

Manage permissions for groups of users

$ groupadd
$ usermod
$ groupmod
$ cat /etc/group
    root:x:0:
    daemon:x:1:
    bin:x:2:
    sys:x:3:
    adm:x:4:
    tty:x:5:
# group name:password or placeholder:GID:member,member,member

Hands-On: Users and Groups¶

Note

To give yourself sudo powers do the following:

Add your user to the wheel group using gpasswd.
As the root user, use visudo and uncomment this line:
```
%wheel  ALL=(ALL)   ALL
```
Save the file and now you should have sudo!

We’ll cover sudo in more depth at a later time.

Create a user on your system for yourself, with your preferred username
Give your user sudo powers
Use use su to get into your user account
Change your password
Create a directory called bootcamp in your home directory
Create a group called devops

What are files?¶

Nearly everything
Files have:
- Owner
- Permissions
- inode
- Size
- Filename

test@x230 ~ $ ls -il
total 8
2884381 drwxrwxr-x 5 test test 4096 Nov  6 11:46 Documents
2629156 -rw-rw-r-- 1 test test    0 Nov 13 14:09 file.txt
2884382 drwxrwxr-x 2 test test 4096 Nov  6 13:22 Pictures

File extensions¶

.jpg, .txt, .doc
Really more of a recommendation
- File contains information about its encoding

$ file $FILENAME # tells you about the filetype

test@x230 ~ $ file file.txt
file.txt: ASCII text

test@x230 ~ $ file squirrel.jpg
squirrel.jpg: JPEG image data, JFIF standard 1.01

ls -l¶

First bit: type
Next 3: user
Next 3: group
Next 3: world
user & group

$ ls -l
drwxrwxr-x 5 test test 4096 Nov  6 11:46 Documents
-rw-rw-r-- 1 test test    0 Nov 13 14:09 file.txt
drwxrwxr-x 2 test test 4096 Nov  6 13:22 Pictures

chmod and octal permissions¶

+=====+========+=======+
| rwx | Binary | Octal |
+=====+========+=======+
| --- | 000    | 0     |
| --x | 001    | 1     |
| -w- | 010    | 2     |
| -wx | 011    | 3     |
| r-- | 100    | 4     |
| r-x | 101    | 5     |
| rw- | 110    | 6     |
| rwx | 111    | 7     |
+=====+========+=======+

u, g, o for user, group, other
-, +, = for remove, add, set
r, w, x for read, write, execute

chown, chgrp¶

user & group

# Change the owner of myfile to "root".
$ chown root myfile

# Likewise, but also change its group to "staff".
$ chown root:staff myfile

# Change the owner of /mydir and subfiles to "root".
$ chown -hR root /mydir

# Make the group devops own the bootcamp dir
$ chgrp -R devops /home/$yourusername/bootcamp

Types of files¶

drwxrwxr-x      5 test    test      4096    Nov  6 11:46 Documents
-rw-rw-r--      1 test    test         0    Nov 13 14:09 file.txt
drwxrwxr-x      2 test    test      4096    Nov  6 13:22 Pictures
----------     -------  -------  -------- ------------ -------------
    |             |        |         |         |             |
    |             |        |         |         |         File Name
    |             |        |         |         +---  Modification Time
    |             |        |         +-------------   Size (in bytes)
    |             |        +-----------------------        Group
    |             +--------------------------------        Owner
    +----------------------------------------------   File Permissions

- is a normal file

d is a directory

b is a block device

ACLs¶

Access control lists
Not recommended; hard to maintain
Typically how other OSes manage permissions
Support depends on OS and filesystem

Hands-On: Files and Permissions¶

$ touch foo # create empty file called foo

As root, create a file in /home/$yourusername/bootcamp
Who can do what to the file?
Make the devops group own the file
Make a file called allperms and give user, group, and world +rwx
Make more files and practice changing their permissions

Package Management¶

Take care of installation and removal of software

Core Functionality:

Install, Upgrade & uninstall packages easily
Resolve package dependencies
Install packages from a central repository
Search for information on installed packages and files
Pre-built binaries (usually)

Popular Linux Package Managers

.deb / APT (used by Debian, Ubuntu)
.rpm / YUM (used by RedHat, CentOS, Fedora)

RPM & yum (RedHat, CentOS, Fedora)¶

RPM

Binary file format which includes metadata about the package and the application binaries as well.

Yum

RPM package manager used to query a central repository and resolve RPM package dependencies.

Yum Commands (Redhat, CentOS, Fedora)¶

We’ll use the tree package as an example below.

# Searching for a package
$ yum search tree

# Information about a package
$ yum info tree

# Installing a package
$ yum install tree

# Upgrade all packages to a newer version
$ yum upgrade

# Uninstalling a package
$ yum remove tree

# Cleaning the RPM database
$ yum clean all

RPM Commands¶

Low level package management. No dependency checking or central repository.

# Install an RPM file
$ rpm -i tree-1.5.3-2.el6.x86_64.rpm

# Upgrade an RPM file
$ rpm -Uvh tree-1.5.3-3.el6.x86_64.rpm

# Uninstall an RPM package
$ rpm -e tree

# Querying the RPM database
$ rpm -qa tree

# Listing all files in an RPM package
$ rpm -ql tree

DPKG & Apt (Debian, Ubuntu)¶

Deb

Binary file format which includes metadata about the package and the application binaries as well.

DPKG

Low level package installer for the .deb file format. Does no package dependency resolution.

Apt

DPKG package manager used to query a central repository and resolve Deb package dependencies. Considered mostly a front-end to dpkg.

Apt Commands (Debian, Ubuntu)¶

Note

You can also use aptitude as a front-end to dpkg instead of apt-get.

# Update package cache database
$ apt-get update

# Searching for a package
$ apt-cache search tree

# Information about a package
$ apt-cache show tree

# Installing a package
$ apt-get install tree

# Upgrade all packages to a newer version
$ apt-get upgrade
$ apt-get dist-upgrade

# Uninstalling a package
$ apt-get remove tree
$ apt-get purge tree

Dpkg Commands¶

Low level package management. No dependency checking or central repository.

# Install or upgrade a DEB file
$ dpkg -i tree_1.6.0-1_amd64.deb

# Removing a DEB package
$ dpkg -r tree

# Purging a DEB package
$ dpkg -P tree

# Querying the DPKG database
$ dpkg-query -l tree

# Listing all files in a DEB package
$ dpkg-query -L tree

Language-specific Package Managers¶

Languages sometimes have their own package management suite
Can be useful for using newer versions of packages
Examples
- pip (Python)
- rubygems (Ruby)
- CPAN (Perl)
- cabal (Haskell)
- npm (NodeJS)
- ... and so on forever ...

Other Package Managers¶

They each fill a specific niche and have their own pros and cons.

Portage (Gentoo) – Source based package installer
pacman (Arch Linux)
ZYpp / Zypper (SUSE) – Yet another RPM package manager

Installing from source¶

Download source tarball, run build scripts and install in a local directory.
RPM/DEB packages do this for you
Not for the faint of heart ... Not recommended!
Using grep as an example

$ wget http://mirrors.kernel.org/gnu/grep/grep-2.15.tar.xz
$ tar -Jxvf grep-2.15.tar.xz
$ cd grep-2.15
$ ./configure
$ make
$ make install

Hands-on: Package Management¶

Install the git package
Query the RPM/APT database for installed packages
List the files in an installed package
Remove the git package

Questions:¶

read example output of ls -al
read output of yum or aptitude search
install a package on their VM/partition (Vim, Git)
- explain what dependencies it also installed