Linux Basics (Day 1)

Today's topics

Announcements

What is a Linux Distribution?

A Linux distribution (often called a distro for short) is an operating system made as a collection of software based around the Linux kernel and often around a package management system. [Wikipedia-distro]
[Wikipedia-distro]http://en.wikipedia.org/wiki/Linux_distribution

Linux beyond the kernel

Early Distributions

_images/slackware-logo.jpg _images/debian-logo.png _images/redhat-logo.png _images/opensuse-logo.png

Slackware

_images/slackware-logo.jpg

Debian

"This is just to announce the imminent completion of a brand-new Linux release, which I'm calling the Debian Linux Release. This is a release that I have put together basically from scratch; in other words, I didn't simply make some changes to SLS and call it a new release. I was inspired to put together this release after running SLS and generally being dissatisfied with much of it, and after much altering of SLS I decided that it would be easier to start from scratch." [Debian-Ian-Murdock] - August 17, 1993
[Debian-Ian-Murdock]http://groups.google.com/group/comp.os.linux.development/msg/a32d4e2ef3bcdcc6

Red Hat

_images/redhat-logo.png

SuSe

_images/opensuse-logo.png

Different approaches

Filling the niches

Each distribution fills a specific niche

Gentoo:source based meta distribution used to create ChromeOS
Android:Mobile platform using the Linux kernel but its own unique userland
OpenWRT:Embedded wifi router distribution
LTSP:Thin client distribution used in some K12 schools
Tails:Security and privacy focused disto that is livecd/usb based
CoreOS:Specialize in massive container deployments

You name it, there's a distro out there!

What we'll be using

CentOS 7

Why?

Linux Basics

What are users?

$ 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

Users have

Managing users

$ cat /etc/passwd
# username:x:UID:GID:GECOS:homedir:shell
$ useradd $USER # vs adduser, the friendly Ubuntu version
$ userdel $USER
$ passwd
_images/xkcd215.png 
# GECOS: full name, office number and building, office phone extension,
# home phone number (General Electric Comprehensive Operating System)
$ chfn # change GECOS information
$ finger # tells you someone's GECOS info

Passwords

user@localhost ~ $ 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

_images/xkcd149.png

Sudo

Consult man 5 sudoers for more information:

# User alias specification
User_Alias  CS312_ADMIN = lance, jordane
User_Alias  CS312_STUDENT = john, jane

# Runas alias specification
Runas_Alias ADMIN = root, sysadmin
Runas_Alias STUDENT = httpd

# Host alias specification
Host_Alias OSU_NET = 128.193.0.0/16
Host_Alias SERVERS = www, db

# Cmnd alias specification
Cmnd_Alias KILL = /bin/kill
Cmnd_Alias SU = /bin/su

#  User privilege specification
root          ALL = (ALL) ALL
CS312_ADMIN   ALL = NOPASSWD: ALL
CS312_STUDENT OSU_NET = (STUDENT) KILL, SU

Acting as another user

$ su joe            # become user joe, with THEIR password
$ su                # become root, with root's password
$ sudo su -         # become root, with your password
$ sudo su joe       # become user joe with your password
_images/xkcd838.png

A dash after su provides an environment similar to what the user would expect. Typically a good practice to always use su -

What are groups?

Manage permissions for groups of users

$ groupadd
$ usermod
$ groupmod
$ gpasswd
$ 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

Users won't be active in new group until they "log back in"

What are files?

Files have:

Owner atime, ctime, mtime
Group POSIX ACLs
Permissions Spinlock
Inode i_ino
Size read, write and link count
Filename   
user@localhost ~ $ ls -il
total 8
2884381 drwxrwxr-x 5 user user 4096 Nov  6 11:46 Documents
2629156 -rw-rw-r-- 1 user user    0 Nov 13 14:09 file.txt
2884382 drwxrwxr-x 2 user user 4096 Nov  6 13:22 Pictures

More file metadata

$ ll
crw-rw-rw- 1 root  tty   5, 0 Jan  6 13:45 /dev/tty
brw-rw---- 1 root  disk  8, 0 Dec 21 14:12 /dev/sda
srw-rw-rw- 1 root  root  0    Dec 21 14:13 /var/run/acpid.socket
prw------- 1 lance lance 0    Jan  5 17:44 /var/run/screen/S-lance/12138.ramereth
lrwxrwxrwx 1 root  root  4    Nov 25 09:26 /var/run -> /run

$ stat /etc/services
  File: `/etc/services'
  Size: 19303       Blocks: 40         IO Block: 4096   regular file
Device: fc00h/64512d  Inode: 525111      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2015-01-07 08:22:43.768316048 -0800
Modify: 2012-05-03 09:01:30.934310452 -0700
Change: 2012-05-03 09:01:30.982310456 -0700
 Birth: -

File extensions

# Tells you about the filetype using magic file data, not file extension
$ file $FILENAME

user@localhost ~ $ file file.txt
file.txt: ASCII text

user@localhost ~ $ file squirrel.jpg
squirrel.jpg: JPEG image data, JFIF standard 1.01

ls -l

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

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 foo dir
$ chgrp -R devops /home/user/foo

Types of files

drwxrwxr-x      5 user    user      4096    Nov  6 11:46 Documents
-rw-rw-r--      1 user    user         0    Nov 13 14:09 file.txt
drwxrwxr-x      2 user    user      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

Package Management

Take care of installation and removal of software

Core Functionality:

Yum vs. Apt

Yum

Apt

RPM & yum (RedHat, CentOS, Fedora)

_images/rpm.png

RPM

Binary file format which includes metadata about the package and the application binaries as well. _images/yum.png

Yum

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

Yum Commands (Redhat, CentOS, Fedora)

# 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

Apt (Debian, Ubuntu)

Friday's Topics

Readings:

Resources