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Rhcsa > Understand and use essential tools > Flashcards

Understand and use essential tools Flashcards

Objective 1 for exam

1
Q

Virtual Console or tty

A

Ctrl + alt + F1 through F6. Ctlr + alt+ F7 will bring back the GUI

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2
Q

cat example

A

cat &laquo_space;EOF > file1
> this is the content
> of file 1
> EOF

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3
Q

cat example 2

A 
cat > file1
this is the content 
of file1
^d
^d(ctrl+d stop entry)
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4
Q

grep examples

A

grep –color ‘root’ /etc/passwd
grep -i ‘root’ /etc/passwd matches case insensitive
grep -v ‘root’ /etc/passwd matches everything but root
grep -n [Aa] text.txt matches upper and lower case
grep ‘^root’ /etc/passwd starts with root
grep ‘root$’ /etc/passwd end with root

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5
Q

generate ssh key

A

use the ssh-keygen command

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6
Q

create a tarball example

A

tar -cvf data.tar dataDir

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7
Q

gzip tar file/directory

A

gzip data.tar creates data.tar.gz

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8
Q

bzip tar file/directory

A

bzip data.tar creates data.tar.bz2

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9
Q

tar with gzip file/directory

A

tar -czvf data.tar.gz dataDir

tar -czvf data.tgz dataDir

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10
Q

tar with bzip2 file/directory

A

tar -cjvf data.tar.bz2 dataDir

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11
Q

extract tar.gz

A

tar -xzvf data.tar.gz

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12
Q

extract tar.bz2

A

tar -xjvf data.tar.bz2

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13
Q

Main Tar command options

A

c(create an archive), x(extract an archive), t(test or list the contents of an archive)

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14
Q

Other tar command options

A

v(verbosity), f(filename), z(for gzip), j(for bzip2)

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15
Q

bzip to uncompress files

A

bunzip abc.tar.bz2

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16
Q

gzip to uncompress files

A

gunzip2 etc.tgz

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17
Q

Star command

A 
More appropriate for archiving files in a SELinux System. It's not installed by default:
# yum install star
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18
Q

Star command to archive a file

A

star -xattr -H=exustar -c -f=home.star /home

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19
Q

star more example to compress a file/directory(ies)

A

star -cv f=archive2.star test-dir

star -xattr -H=exustar -c -f=files.star file{1,2,3}

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20
Q

Star extract file/directory(s) example

A

star -xv f=/tmp/archive2.star

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21
Q

star list files in an archive file

A

star -tv f=/tmp/archive2.star

22
Q

Text editors

A

Vi(Preferred)
gedit(GUI)
nano(text editor)

23
Q

Create a hard link

A

ln filetolink desktop/file

24
Q

Create a symlink

A

ln -s filetolink desktop/filelink

25
Q

To view inode #

A

ls -li file

26
Q

Hard link

A

a pointer to a file’s inode

27
Q

soft link (symlink)

A

a pointer to a file

28
Q

Linux ugo/rwx permissions

A

read (r)
write(w)
execute(x)

29
Q

Octal value for permission bit

A 
read = 4
write = 2
execute = 1
No permission(or dash "-") = 0
30
Q

Umask command

A 
The default permission in RHEL comes from the umask or user file creation mode mask value. run the umask command to see your default umask value:
# umask
31
Q

Umask value obtained

A

From the /etc/profile script

32
Q

File default umask

A

666

33
Q

Directory default umask

A

777

34
Q

Calculate umask of a file

A

subtract default file umask (666) from current user’s umask(0022) = 0644

35
Q

Calculate umask of a directory

A

subtract default directory umask(777) from current user’s umask(0022) = 0755

36
Q

set the immutable bit

A

chattr +i file

37
Q

view attributes of a file

A

lsattr file

38
Q

immutable bit

A

It helps prevent accidental deletion. Review man 1 chattr to learn more attributes which can be applied to a file

39
Q

attributes that can be added to a file

A

(acdeijstuADST), a = append only, c = compressed, d = no dump, e = extent format, i = immutable, j = data jornaling, s = secure deletion, t=no-tail-merging, u = undeletable, A = no atime updates, D = synchronous directory updates, S= synchronous updates, T = top of directory hierarchy.

40
Q

chattr options

A
  • R = recursively
  • V = verbose
  • f = suppress most error messages
  • v = set the file version(generation number)
41
Q

Managing Permissions from gui

A

You can use the Nautilus file management tool
– right click on a file or folder > select properties > click on the permission Tab.
– Or launch Nautilus from the command line:
# Nautilus &

42
Q

Special permissions

A

Setuid or setgid permission of an executable means that the command will run as the user(or group) of the file, not as the user that ran it.
The sticky bit for a directory sets a special restriction on deletion of files: only the owner of the file and root can delete within the directory, example is /tmp

43
Q

special permissions effect on files

A

U+s (SUID) - file executes as the user that owns the file, not the user that ran the file.
G+s(SGID) - file executes as the group that owns the file.
o+t(sticky) - no effect on file

44
Q

Special permissions effect on directories

A

U+s(SUID) - no effect on directory
G+s(SGID) - files newly created in the directory have their group owner set to match the group owner of the directory.
O+t(sticky) - users with write on the directory can only remove files that they own, they cannot remove files owned by other users

45
Q

Setting special permissions

A 
Symbolically: setuid = u+s, setgid = g+s, sticky = o+t
Numerically: (fourth preceding digit) setuid = 4; setgid = 2; sticky = 1.
# chmod 4770 file
# chmod 2770 dir
# chmod g+s dir
46
Q

to search for unknown man pages

A 
# man -k lvm
# apropos lvm
# whatis nfs
or you can run ls on /usr/share/doc
47
Q

no output from man pages

A 
First check for the package
# rpm -qa man
then if it's installed run:
# makewhatis &
48
Q

info pages

A

Similar to man pages, also over
# info -k lvm
info pages are located in /usr/share/info

49
Q

Man pages sections and meanings

A

1 ———– user commands
2 ———- Kernel System calls (entry points to the kernel from userspace)
3 ———- Library functions
4 ———- Special files and devices
5 ———- file formats and conventions
6 ———- Games
7 ———- Conventions, standard, and miscellaneous pages
8 ———- System administration commands
9 ———- Linux kernel HPI (internal kernel calls), this is recent

50
Q

Access remote system using VNC

A

$ yum install tigervnc-server </code>
This puts a config file on your remote machine in /etc/sysconfig/vncservers
edit this file and add:
VNCSERVERS=”2:myusername”
VNCSERVERARGS[2]=”-geometry 800x600 -nolisten tcp -nohttpd”
Aside from changing “username” you want it to look like this. All we did to change it, is remove the “-localhost” directive. This would have restricted us from connecting from a remote system without a tunnel setup. Since this is an exam and not the real world, we can disable that.

Set up your password on the remote machine by running
$ vncpasswd</code>

And finally start your vncserver
$ vncserver :1</code>

The output should look like this:
[root@rhel6 ~]# vncserver :1
New ‘rhel6.local:1 (root)’ desktop is rhel6.local:1<br></br>
Starting applications specified in /root/.vnc/xstartup<br></br>
Log file is /root/.vnc/rhel6.local:1.log

The default vnc client on Red Hat Enterprise Linux 6 is tigervnc. If it is not already installed on the system:
$ yum install tigervnc</code>

To connect to the newly setup vncserver just type:
$ vncviewer rhel6.local:5901
(replace rhel6.local with your remote host)

51
Q

create SSH Keys and change permissions(example)

A 
$sudo su - username
$ cd .ssh
$ssh-keygen -t rsa   
$cat id_rsa.pub > authorized_keys
$cp id_rsa authorized_hosts
$chmod 644 $HOME/.ssh/authorized_hosts
$chmod 700 $HOME/.ssh

Test
$ssh host

Rhcsa (9 decks)

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