ACL

ACL

ACL stands for active control list. This is the part of the file that allows you to choose who specificly can assess the file not just the user or group who created it. this is incredibly useful for keeping that guy in the office out of your files.

GETFACL

the getfacl command is the command used to show you what acls are already used in the files it should look like this:
a    # file: my_stuff
b    #owner: jjohnson
c    #group: root
d    user: :rwx
e    user:steve:---
f     group: :r-x
g     mask: :r-x
h     other: :r-x

as you can see line a shows the file name line b and c show the owner and the group and the last lines show what the specified groups or users can and cannot do for instance Steve cannot do anything to this file so he can't look through my stuff.

SETFACL

now how do you add acls to a file? you use setfacl
say for instance your new intern john is looking into your important_stuff folder

what you do is use:

setfacl

with the modify option command

setfacl -m

then you add the acl

setfacl -m u:john:0

lastly you add the file name

setfacl -m u:john:0 important_stuff

hit enter and you have successfully kept intern john out of the important stuff folder.

lvcreate

Logical volumes:
Before we start making logical volumes we have to know what a logical volume is. A logical volume is a portion of a volume group witch is in turn an abstract representation of your physical volumes (hard drives). this allows you to treat your storage as one single volume and partition it however you see fit across hard drives.

a quick diagram of physical volumes, volume groups and logical volumes

making logical volumes is simple albeit dangerous. if you make a typo you can seriously bork the computer. first the command you want to use is lvcreate with its two most basic options -n and -L.

lvcreate -n var -L 20GiB

-n is the name option it allows you to give a name to the new partition.

-L is the size partition it allows you to choose how big the partition has to be

--you can see your logical partitions if you use the command lvdisplay--

after you have created your partition you will have to make the file system for the partition to do this you just use the command mkfs or make files system like this

mkfs <the partitions address>

--to find the partition address all you have to do is look in lvcreate it should look like any file system address--

once you have done that you have to mount it to do this you mount it like any other file system

mount <the partition's address> <directory were you want it mounted>

scheduling tasks

at

at allows you to run commands once at a different chronological location than when you type them. for instance you can run:

$ at 11:50
and it will open a terminal that will allow you to type in a command that will be executed at 11:50 

crontab

crontab allows you to run a repeating command at a different time or date every time that time or date happens. to do this you have to use the command:
$ crontab -e
this allows you to edit the crontab. then you can schedule tasks by typing in the time code then the command. the time codes are formatted like this:

minute hour day week month year

so for instance Wednesday march 16th at 7:30 at night would be:

30 19 16 3 3

for any random unit of time you use a *. so for say every wednesday at 7:00 AM you would use:

0 7 * * 3

now how do you find out what cron tabs are running?  all you have to do is use:

$ crontab -l

AT

at is a great command that you can use to activate commands at another time.

to use at  all you have to do is type at and the time:

$ at 15:00

this will change the dollar signs to

at>

then you can type the commands into the console

then to exit the console by hitting ctrl-D

useradd/passwd/usermod

User add/passwd/usermod

This is one of the most important commands to learn

what does it do?:
it allows you to create users

so say for example you wanted to make an account for bruce wayne:

sudo useradd bruce_wayne  -m

 the -m here tells the computer to create a home directory if it does not exist
you can also use:  -M to tell the computer not to create a home directory for the user

but that is not too secure because there is no password to do this we use passwd

sudo passwd bruce_wayne 

for this demonstration we are using 'batman' as the password

 what if you dont want the password to stay the same for too long? then you use -e: 

-e tells the computer when this user account password will expire

this date is the amount of seconds from the epoch or 1/1/1970 this is because that was the year UNIX was officially invented.

we are going to use October 5th 2277 in UNIX that is: 9693475200

sudo useradd bruce_wayne  -m -e 9693475200

Unfortunately -e presents us with a problem what do you do a user account is inaccessible for too long? You use -f. -f tells the computer how long this account's password can be expired before it deletes the account. this is presented as days before the user account will terminate itself. for this we are going to give this a week

sudo useradd bruce_wayne  -m -e 9693475200 -f 7


groups:

groups are a big part of user management. so it makes sense that there are group tools inside of useradd.

first how do we designate the group a user is in? we use -g. -g sets the name or number of the group that the user will be created in. 


sudo useradd bruce_wayne  -m -e 9693475200 -f 7 -g 'justice league'

if you want the user to be part of more groups you use -G. -G sets the names of the other groups this user is a part of.


sudo useradd bruce_wayne  -m -e 9693475200 -f 7 -g 'justice league' -G 'detective comics'

you can even have it create a group with the same name as the user with -n


sudo useradd bruce_wayne  -m -e 9693475200 -f 7 -g 'justice league' -G 'detective comics' -n

these are some other useful options: 
---------------------------------------------------------------------------------------------------------------------------------
-b this tells the computer what the base directory will be or in plainer English what directory you start in on this account.

-c allows you to connect any text string as a description for the user

-h help  tells the computer to display the help message and exit

-l this tells the computer to not have the user added to the last login file.

-r this is used to flag the account as a user account

-s tells the computer a login shell that the account will use

-u allows you to choose the user id for the account

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 User mod:

so after you make your account how are you going to edit the user? Well you use Usermod!

here are some options on usermod


-a, allows you to add the user to the following group

-c, this is used to change the comment in the passwd folder

-d, this changes the users home directory to the following group

-e, his changes the user's password experation date

-f, this changes the number of days that the user account can be expired before deletion

-g, his changes the users initial group

-G, this allows you to add the user to the following groups

-l,  this changes the name of the user

-L, his locks the user's password

-m, his allows you to move the users home directory

-o, When used with the -u option, allows to change the user ID to a non-unique value 

 

-s, this changes the users login shell

-u, this changes the users UID

-U, this unlocks a user password

Cut

Cut is a command that allows you to output certain portions of the line. it gives you many ways to do this:

delimiters and field lists:

delimiters and field lists allow you to chunk out lines separated by characters for instance:
head -n 1 etc/passwd/ |cut -d ':' -f 1
outputs:
root

as you can see -d is the delimiter and -f is the field list. here the character they are separated by is ':' and the section they are showing is 1. you can even use -s to bypass lines that dont contain field delimiters

charicters:

characters are the simplest way to use cut. it just outputs the characters in a range. for example:

head -n 1 etc/passwd/ |cut -c 2-4
outputs:
oot

as you can see -c is the character range.

bytes:

bytes allows you to specify the amount of bytes you want the output to take up. I am not going to give an example for this. all you need to know is that -b is bytes. 

Heads/ Tails

Head and tail  are two simple commands.

 the first one head gives the first ten lines of a file for instance:

head /etc/passwd
outputs:
root
bin
deamon
adm
lp
sync
shutdown
halt
mail

the secon
root
bin
deamon
adm
lp
d one: tail gives the last ten words of a file to use a similar example:

tail /etc/passwd
outputs:
avahi
tcpdump
jelkner
student
systemd-bus-proxy
systemd-network
geoclue
setroubleshoot
jjohnson
hrodriguez





now people dont always want just the first or last ten words in a line. sometimes they want the first/last four or first/last twenty seven. to do this we use the:

-N parameter 

the -n parameter tells the computer how many lines you want it to output for instance:

head -n 5 /etc/passwd

gives you:
root
bin
deamon
adm
lp

or
tails -n 15 /ect/passwd

gives you:
pulse
gdm
gnome-initial-setup
postfix
sshd
avahi
tcpdump
jelkner
student
systemd-bus-proxy
systemd-network
geoclue
setroubleshoot
jjohnson
hrodriguez

today I mostly re set up my test space folder to practice file manipulation with the command line. however given how rusty I became with only three days break from the command line: do you know any practical things I can do in my everyday life to practice?

Review Questions

1. You do not want to buy a RHEL license, but you want to create an environment to practice for the exam. Which distribution should you use?

A: centos

2. Why can’t you use a 32-bit version of RHEL to prepare for the exam?

3. You want to install a minimal system. How much RAM do you need?

A: 512 MB

4. Why is it a good idea to have Internet access on all servers you are installing?

5. You want to install a virtual machine on a computer that does not have an optical disk drive. What is the easiest alternative to perform the installation?

A: download a disk formated file

6. Why is it a good idea to install a GUI?

A: there are some easy tools that can help you with the problems on the RHCSA

7. What is the default file system on RHEL 7?

A:LVM

8. Can you install RHEL if you do not have Internet access?

A: yes

9. What is the most important feature offered through RHN?

A: technical support

10. Which installation pattern should you use if you have a very limited amount of disk space available?