LFCS Exam Guide
-----------------du------------------------------------------------
$ sudo du --max-depth=1 -hx /
$ sudo du -sh /
-----------------Ulimit------------------------------------------------
Ulimit -a
$ ulimit -H -n
$ ulimit -S -n
$ ulimit -n 1600
/etc/security/limits.conf then reboot.
@<group> hard nproc <value>
<user> soft nproc <value>
## Example hard limit for max opened files
marin hard nofile 4096
# vi /root/.bashrc limit of processes for the super-user root to be unlimited
ulimit -u unlimited
$ ulimit -u unlimited
-----------------nice------------------------------------------------
$ nice -n 5 command [ARGS]
$ nice -5 command [ARGS]
$ nice
$ nice cat &
$ ps -l
$ renice +5 -p 20003
-----------------Opened files------------------------------------------------
-----------------grep------------------------------------------------
------------------dpkg-----------------------------------------------
$ dpkg -l List all packages installed:
$ dpkg -L wget List files installed in the wget package:
$ dpkg -s wget Show information about an installed package:
$ dpkg -I webfs_1.21+ds1-8_amd64.deb Show information about a package file:
$ dpkg -c webfs_1.21+ds1-8_amd64.deb List files in a package file:
$ dpkg -S /etc/init/networking.conf Show what package owns /etc/init/networking.conf:
$ dpkg -V package Verify the installed package's integrity:
$ sudo dpkg -i foobar.deb Installing/Upgrading
$ sudo dpkg -r package remove all of an installed package except for its configuration files
$ sudo dpkg -P package remove all of an installed package, including its configuration files
------------------apt-----------------------------------------------
$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get -u upgrade
$ apt-cache search "kernel"
$ apt-cache search -n "kernel"
$ apt-cache pkgnames "kernel"
$ sudo apt-get install apache2-dev
$ apt-cache search bash
$ apt-cache search -n bash
$ apt-cache show bash basic information about the apache2 package
$ apt-cache showpkg apache2 detailed information about the apache2 package
$ apt-cache depends bash Lists all dependent packages for apache2:
$ apt-cache rdepends bash
$ sudo apt-get remove [package] remove a package from the system (this does not remove the configuration files)
$ sudo apt-get --purge remove [package] remove a package and its configuration files from a system
-------------------Crontab------------------------------------------------------------------------------------------
*/1 * * * * pkill "scan_filesystem" > /root/exam/output.log 2>&1
0 0 1 1 * Run once a year at midnight on January 1
0 0 1 * * Run once a month at midnight on the first day of the month
0 0 * * 0 Run once a week at midnight on Sunday morning
0 0 * * * Run once a day at midnight
0 * * * * Run once an hour at the beginning of the hour
@reboot Run at startup (of the cron daemon)
10 16 * * * runs a command at 4:10 PM
0 2 * * 6 runs a command at 2:00 AM on Saturday
0 0 1 1 0 runs at midnight on New Years Day (January 1st)
0 * * * * runs every hour
*/15 * * * * runs every 15 minutes
*/30 * * * * runs every 30 minutes
*/10 * * * * runs every 10 minutes
0 17-18 20 * * At minute 0 past every hour from 17 through 18 on day-of-month 20
--------------------MBR-Disk---------------------------------------------
blkid
lsblk
$ dd if=/dev/sda of=mbrbackup bs=512 count=1 backup the MBR (along with the partition table)
$ sudo dd if=mbrbackup of=/dev/sda bs=512 count=1 Restore MBR
$ sudo fdisk /dev/sdb fdisk
$ sudo partprobe -s
fsck /dev/sda The system will not use the new partition table until you reboot. However, you can
--------------file full of zeros 1 GB---------------------------------------------------
$ dd if=/dev/zero of=imagefile bs=1M count=1024 Create a file full of zeros 1 GB in length
$ mkfs.ext4 imagefile
$ mkdir mntpoint
$ sudo mount -o loop imagefile mntpoint
$ sudo umount mntpoint
---------------fdisk--------------------------------------------------
$ sudo fdisk -C 130 imagefile
m
Command (m for help): n
Command (m for help): p
Command (m for help): w
$ sudo mkfs -t ext4 /dev/sda10
$ sudo mkfs.ext4 /dev/sda10
$ mkfs.ext4 /dev/sda1 -L ROOT Label while formating
$ sudo fsck -t ext4 /dev/sda10
$ sudo fsck.ext4 /dev/sda10
$ sudo fsck /dev/sda10
$ mount -t ext /dev/sdb4 /home
$ umount /home
$ umount /dev/sda3
$ sudo mount -t nfs myserver.com:/shdir /mnt/shdir
myserver.com:/shdir /mnt/shdir nfs rsize=8192,wsize=8192,timeo=14,intr 0 0 fstab
$ mount -a
---------------Attributes--------------------------------------------------
$ lsattr filename
$ chattr [+|-|=mode] filename
i: Immutable
a: Append-only
d: No-dump
A: No atime update
----------------Quota-------------------------------------------------
sudo apt update
sudo apt install quota
sudo apt install linux-image-extra-virtual
# vim /etc/fstab
/dev/VolGroup00/LogVol02 /home ext3 defaults,usrquota,grpquota 1 2
$ sudo mount -o remount,usrquota,grpquota /
umount /mount-point
mount /file-system /mount-point
mount /dev/vdb1 /work
# quotacheck -cug /home
# quotacheck -avug
# edquota username
# quota username
# edquota -g devel
# quota -g devel
$ sudo edquota -u user Configure Quotas for a Single User
# quotaoff -vaug
# quotaon -vaug
# quotaon -vug /home
# repquota /home
# repquota -a generate report
-------------LVM----------------------------------------------------
# fdisk -cu /dev/sda
n
p
t
1
8e
w
$ partprobe -s
# pvs
# pvcreate /dev/sda1 /dev/sdb1 /dev/sdc1
# pvs
# vgs
# vgcreate tech_add_vg /dev/sda1 /dev/sdb1 /dev/sdc1
# vgs
# vgdisplay tech_add_vg
# lvs
# lvcreate -L 18G -n tech_documents tech_add_vg
# lvs
# mkfs.ext4 /dev/tech_add_vg/tech_documents
# mount /dev/tech_add_vg/tech_documents /mnt/tech_documents/
# df -h
# cat /etc/mtab
# vim /etc/fstab
/dev/mapper/tech_add_vg-tech_documents /mnt/techt_documents ext4 defaults 0 0
# mount -av
-----------SWAP------------------------------------------------------
swapoff -v /dev/VolGroup00/LogVol01
$ swapoff -a
# lvextend -L +2G /dev/mapper/fedora_studentvm1-swap
mkswap /dev/VolGroup00/LogVol01
swapon -va or sudo swapon /swapfile
$ swapon -a
vim /etc/
/dev/sdaY swap swap defaults 0 0
cat /proc/swaps
free
-------------RAID-mdadm----------------------------------------------------
$ sudo apt-get update -y
$ sudo apt-get install -y mdadm
$ sudo fdisk /dev/sdb
$ sudo fdisk /dev/sdc
$ sudo mdadm --create /dev/md0 --level=1 --raid-disks=2 /dev/sdbX /dev/sdcX
$ sudo mkfs.ext4 /dev/md0
$ sudo bash -c "mdadm --detail --scan >> /etc/mdadm.conf"
$ sudo mkdir /myraid
$ sudo mount /dev/md0 /myraid
$ vim /etc/fstab
/dev/md0 /myraid ext4 defaults 0 2
$ cat /proc/mdstat
$ sudo mdadm -S /dev/md0 to stop the RAID device.
$ sudo systemctl start mdmonitor
$ sudo systemctl enable mdmonitor
$ sudo mdadm --create /dev/md0 -l 5 -n3 -x 1 /dev/sda8 /dev/sda9 /dev/sda10 /dev/sdb2 To create a hot spare when creating the RAID array
----------------------RAID-mdadm-------------------------------------------
$ sudo fdisk /dev/sda
partprobe
$ sudo mdadm -C /dev/md0 --level=1 --raid-disks=2 /dev/sdaX /dev/sdaY
$ sudo mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sda /dev/sdb /dev/sdc
$ sudo mkfs.ext4 /dev/md0
$ sudo mkdir /myraid
$ sudo mount /dev/md0 /myraid
$ vim /etc/fstab
/dev/md0 /myraid ext4 defaults
$ sudo bash -c "mdadm --detail --scan >> /etc/mdadm.conf"
$ cat /proc/mdstat
Add a new disk
# mdadm --manage /dev/md0 --add /dev/sdd1
# mdadm --detail /dev/md0
-----------cryptsetup-Encryption------------------------------------------------------
$ apt-get update
$ apt-get install cryptsetup
$ modprobe dm_crypt
$ sudo fdisk /dev/sda
$ sudo partprobe -s
$ sudo cryptsetup luksFormat /dev/sda4
$ sudo cryptsetup luksOpen /dev/sda4 secret-disk
$ vim /etc/crypttab
secret-disk /dev/sda4
$ sudo mkfs -t ext4 /dev/mapper/secret-disk
$ sudo mkdir -p /secret
$ vim /etc/fstab
/dev/mapper/secret-disk /secret ext4 defaults
$ sudo mount /secret
$ sudo mount -a
reboot
----------------virsh-------------------------------------------------
virsh
https://ostechnix.com/manage-kvm-virtual-machines-with-virsh-program/
$ qemu-img convert -O vmdk myvm.qcow2 myvm.vmdk Convert format
$ grep -e vmx -e svm /proc/cpuinfo check that you have hardware virtualization available and enabled
$ sudo systemctl stop vmware
$ sudo systemctl disable vmware
$ sudo systemctl stop vboxdrv
$ sudo systemctl disable vboxdrv
$ sudo systemctl start libvirtd
$ sudo virt-manager
tc-install
$ sudo qemu-img create -f qcow2 /var/lib/libvirtd/myimg.qcow2 24M
$ sudo qemu-system-x86_64 -hda /var/lib/libvirtd/myimg.qcow2 \ -cdrom /teaching/LFCW/RESOURCES/LFS201/CorePlus-current.iso -usbdevice tablet
----------------PAM-------------------------------------------------
/etc/pam.d
-----------------hostnamectl------------------------------------------------
$ hostname
$ sudo hostname lumpy
$ sudo hostnamectl set-hostname lumpy
$ hostnamectl
------------ip link-----------------------------------------------------
$ ip link show
$ ip -s link show eth0
$ sudo ip addr add 192.168.1.7 dev eth0
$ sudo ip link set eth0 down
$ sudo ip link set eth0 mtu 1480
$ sudo ip route add 172.16.1.0/24 via 192.168.1.5
--------------ifconfig---------------------------------------------------
$ ifconfig
$ ifconfig eth0
$ sudo ifconfig eth0 192.168.1.50
$ sudo ifconfig eth0 netmask 255.255.255.0
$ sudo ifconfig eth0 up
$ sudo ifconfig eth0 down
$ sudo ifconfig eth0 mtu 1480
$ sudo ip link set eth0 down OR $ sudo ifconfig eth0 down
/etc/sysconfig/network OR /etc/networking/interfaces
iface eth0 inet static
address noted from step1
netmask noted from step1
gateway noted from step1
$ sudo ip link set eth0 up OR $ sudo ifconfig eth0 up
$ sudo cp resolv.conf.keep /etc/resolv.conf
$ cat /etc/hosts
192.168.1.180 mysystem.mydomain
127.0.0.1 ad.doubleclick.net
$ wget http://winhelp2002.mvps.org/hosts.txt
$ sudo sh -c "cat hosts.txt >> /etc/hosts"
$ ping yourhostname
$ sudo reboot
$ ping hostname
--------------nmcli-add another ip---------------------------------------------------
$ sudo nmcli con obtain your current internet address and interface name
$ sudo nmcli con show "Auto Ethernet" | grep IP4.ADDRESS
$ nmcli con show 1c46bf37-2e4c-460d-8b20-421540f7d0e2
$ sudo nmcli con show "Auto Ethernet" | grep IP4.ADDRESS
$ sudo nmcli con modify "Auto Ethernet" +ipv4.addresses 172.16.2.140/24
$ sudo nmcli con up "Auto Ethernet"
$ sudo nmcli con modify "Auto Ethernet" -ipv4.addresses 172.16.2.140/24
$ sudo nmcli con up "Auto Ethernet"
--------------nmcli-add another route---------------------------------------------------
$ route
$ ip route
$ sudo nmcli conn mod "Auto Ethernet" +ipv4.routes "192.168.100.0/24 172.16.2.1"
$ route
$ sudo nmcli conn up "Auto Ethernet"
$ route
$ sudo nmcli conn mod "Auto Ethernet" -ipv4.routes "192.168.100.0/24 172.16.2.1"
$ sudo nmcli conn up "Auto Ethernet"
----------------firewall-cmd-------------------------------------------------
$ sudo systemctl [enable/disable] firewalld
$ sudo systemctl [start/stop] firewalld
$ sudo systemctl status firewalld
$ sudo firewall-cmd --state
$ sudo firewall-cmd --get-default-zone Get the default zone:
$ sudo firewall-cmd --get-active-zones Obtain a list of zones currently being used:
$ sudo firewall-cmd --get-zones List all available zones:
$ sudo firewall-cmd --set-default-zone=trusted To change the default zone to trusted and then change it back!
$ sudo firewall-cmd --set-default-zone=public then change it back
$ sudo firewall-cmd --zone=internal --change-interface=eno1 To assign an interface temporarily to a particular zone:
$ sudo firewall-cmd --permanent --zone=internal --change-interface=eno1 To assign an interface to a particular zone permanently:
$ sudo firewall-cmd --get-zone-of-interface=eno1 To ascertain the zone associated with a particular interface:
$ sudo firewall-cmd --zone=public --list-all Finally, to get all details about a particular zone:
man firewalld-cmd
$ sudo firewall-cmd --zone=home --add-port=21/tcp
$ sudo firewall-cmd --zone=home --list-ports
$ grep " 21/tcp" /etc/services
$ which firewalld firewall-cmd
$ sudo apt-get install firewalld
$ tar xvf firewalld-0.3.13.tar.bz2
$ cd firewalld-0.3.13
$ ./configure
$ make
$ sudo make install
$ sudo make uninstall
$ firewall-cmd --help
$ sudo firewall-cmd --zone=public --add-service=http Adding Services to a Zone --permanent
$ sudo firewall-cmd --zone=public --add-service=https Adding Services to a Zone --permanent
$ sudo firewall-cmd --list-services --zone=public
$ sudo firewall-cmd --reload
$ sudo firewall-cmd --list-services --zone=public
--permanent
-------------------grub-run level----------------------------------------------
/etc/default
/etc/default/useradd
$ sudo shutdown -r now Reboot the system using shutdown
$ sudo shutdown -h now Power off the system usingshutdown
/etc/default/grub
/etc/grub.d
$ sudo grub2-install /dev/sda
$ sudo systemctl start gdm
$ sudo systemctl start lightdm
$ sudo telinit 5
$ sudo service gdm restart
$ sudo service lightdm restart
# update-grub
----------tar------------------------------------------------------------------------------------
tar -cfvj archive.tar.bz2 file1 file2
tar -xfvj archive.tar.bz2
tar -cfvz archive.tar.gz file1 file2
tar -xfvz archive.tar.gz
tar -cvf archive.tar file1 file2
tar -xvf archive.tar
------------diff----------------------------------------------------------------------------------
$ cmp file1 file2
$ diff file1 file2
$ diff -q directory-1/ directory-2/
--------------vim--------------------------------------------------------------------------------
100G Jump to line 100
dd delete
10G Jump to line 10
p Paste
ww Save
--------------input-output-redirection---------------------------------------------------
$ cat music.mp3 > /dev/audio
Mail -s "Subject" to-address < Filename
$ myprogram 2>errorsfile
find . -name 'my*' 2>error.log
ls Documents ABC> dirlist 2>&1
-------------Links---------------------------------------------------------------------------------
$ ln topprocs.sh tp
$ find -type f -links +1
ls -i Files that are hard-linked together share the same inode number
$ ln -s /bin/topprocs.sh topps.sh
unlink symlink_name
------------find------------------------------------------------------------------------------------------------------------
1. Searching for files and directories named gcc:
$ find /usr -name gcc
2. Searching only for directories named gcc:
$ find /usr -type d -name gcc
3. Searching only for regular files named gcc:
$ find /usr -type f -name gcc
4. To find and remove all files that end with .swp:
$ find -name "*.swp" -exec rm {} \;
5. To find files based on time:
$ find / -ctime 3
6. To find files based on sizes:
$ find / -size 0
7. To find files greater than 10 MB in size and running a command on those files:
$ find / -size +10M -exec command {} \;
8. Find Files With 777 Permissions:
# find . -type f -perm /0777 -print
9. Find Executable Files:
find <dir> -executable -type f
find / -perm /a=x
10. find and delete all empty directories:
find /path/to/dir -empty -type d -delete
find /path/to/dir -empty -type f -delete
11. cp -p $(find /root/test5/ -type f -perm /6000) /root/test6/
12. # find /root/test5/ -type f -perm /u=s,g=s
13. $ find . -size 6M
14. $ find . -size +2G
15. $ find . -size -10k
16. # find . -size +10M -size -20M
17. find . \! -user foo -print
18. find /tmp/systemd-private-apache2/tmp/ -type f -name "magick-*" -mtime +1 -delete
19. find /root/exam/ -type f -name "*.txt" \! -user test1 -perm 0777 -exec cp -r {} /root/exam/test/ \;
20. Find the init.d directory, starting from /, and then create a symbolic link from within your home directory to this directory
student:/tmp> find / -type d -name init.d
student:/tmp> cd ~
student:/home/student> ln -s /etc/init.d .
--------user management--------------------------------------------------------------------------------------
0 - no permission
1 - execute
2 - read
4 - write
4777 = u+s suid
2777 = g+s sgid
1777 = +t stickybit
ls -l /etc/skel/
adduser user
$ sudo useradd -m -d /home/bob1 bob1
usermod -a -G group user
chown -R user:group /file
chgrp group filename
chown USER FILE
getent group
groupadd group-name
sudo groupdel staff
# groups gp-name
# group
# gpasswd -d user group Remove a User from a Group in Linux
# groups user
cat /etc/shells
# usermod --shell /bin/bash user
# vi /etc/passwd
---------------ENV-Variable--------------------------------------------------------------------------------------------
export NAME=VALUE
export JAVA_HOME=/opt/openjdk11
echo $JAVA_HOME
sudo nano ~/.bashrc
export [VARIABLE_NAME]=[variable_value]
export APACHE_RUN_USER="www-data"
$ source .bashrc
OR
export PATH=$PATH:/myNewDir
-------------Container--------------------------------------------------------------------------------------------------
$ docker rm $(docker ps -a -q) Delete all un used containers
$ sudo apt-get install docker.io
sudo systemctl start docker
sudo systemctl status docker
$ sudo docker search apache Search for the httpd container
$ sudo docker pull docker.io/httpd Retrieve the container
$ sudo docker images List the installed containers
# docker tag httpd aby Change tag name
$ sudo docker images --all List the components associated with the images
sudo docker run httpd Start the httpd dockercontainer
# docker run -d httpd Start the httpd docker container in background
$ elinks http://172.17.0.2
sudo docker ps Stop the container anddockerservice and clean up
sudo docker stop b936b0afeb23 Stop the container anddockerservice and clean up
# docker rmi -f aby Remove container
sudo docker rmi -f docker.io/httpd If you do not need to reuse them you can clean up
sudo docker system prune -a Deleted Containers
sudo systemctl stop docker
--------------apache------------------------------------------------------------------------------------------------------
# apt-get install apache2
# /etc/init.d/apache2 start
# /etc/init.d/apache2 status
# /etc/init.d/apache2 restart
# vim /etc/apache2/sites-available/yourdomain.com.conf
<virtualhost *:80="">
ServerAdmin webmaster@localhost
ServerName yourdomain.com
ServerAlias www.yourdomain.com
DocumentRoot /var/www/yourdomain.com
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
</virtualhost>
$ sudo a2ensite yourdomain.com.conf
$ sudo a2dissite 000-default.conf
# mkdir /var/www/yourdomain.com
# vi /var/www/yourdomain.com/index.html
# sudo systemctl restart apache2
http://yourdomain.com
----------sysctl-------------------------------------------------------
$ sysctl -a List kernel parameters
$ ls -l /proc/sys/kernel/ Location
$ sudo sysctl net.ipv4.ip_forward=1 Change Value
sysctl net.ipv4.icmp_echo_ignore_all Paramater Info
----------lsmod-------------------------------------------------------
uname -r
lsmod lsmod to list the loaded modules
/lib/modules/$(uname -r)/modules.dep.
$ sudo insmod /lib/modules/$(uname -r)/kernel/drivers/net/ethernet/intel/e1000e.ko Directly load modules
$ modinfo e1000e modinfo to display information about a module
$ modprobe e1000e modprobe to load a module
$ modprobe -r e1000e modprobe -r to unload or remove a module
dmesg -w
-----------udev------------------------------------------------------
Create and implement a rule on your system that will create a symlink calledmyusbwhen aUSBdevice is plugged in
$ cat /etc/udev/rules.d/75-myusb.rules
SUBSYSTEM=="usb", SYMLINK+="myusb"
Plug in a device
ls -lF /dev | grep myusb
umount /media/whatever
$ ls -lF /dev | grep myusb
----------Adding a New Startup Service with systemd-------------------------------------------------------
Some Other Useful Information
--------------------Methods of bringing down the GUI:-----------------------------------------------------------
student:/tmp> sudo systemctl stop gdm
student:/tmp> sudo systemctl stop lightdm
student:/tmp> sudo telinit 3
Methods of bringing the GUI back up:
student:/tmp> sudo systemctl start gdm
student:/tmp> sudo systemctl start lightdm
student:/tmp> sudo telinit 5
-----------------reboot/halt/poweroff----------------------------------------------------------------------------------
reboot the system is to use the shutdown command.
The halt and poweroff commands issue shutdown -h to halt the system
reboot issues shutdown -r and causes the machine to reboot instead of just shutting down
When administering a multi-user system, you have the option of notifying all users prior to shutdown, as in:
$ sudo shutdown -h 10:00 "Shutting down for scheduled maintenance."
---------------Locating Applications----------------------------------------------------------------------------------
$ which diff
$ whereis diff
---------------Accessing Directories-----------------------------------------------------------------------------------
pwd Displays the present working directory
cd ~ or cd Change to your home directory (shortcut name is ~ (tilde))
cd .. Change to parent directory (..)
cd - Change to previous directory (- (minus))
cd / Changes your current directory to the root (/) directory (or path you supply)
ls List the contents of the present working directory
ls –a List all files, including hidden files and directories (those whose name start with . )
tree Displays a tree view of the filesystem
tree -d / tree view
-----------Hard Links---------------------------------------------------------------------------------------------------
If you remove either file1 or file2 in the example, the inode object (and the remaining file name) will remain, which might be undesirable, as it may lead to subtle errors later if you recreate a file of that name.
$ ln file1 file2 Suppose that file1 already exists. A hard link, called file2, is created with the command
$ ls -li file1 file2
$ ls -li file1?
-------------Soft (Symbolic) Links------------------------------------------------------------------------------------
Soft (or Symbolic) links are created with the -s option, as in:
$ ln -s file1 file3
$ ls -li file1 file3
--------------Navigating the Directory History---------------------------------------------------------------------
The cd command remembers where you were last, and lets you get back there with cd -
For remembering more than just the last directory visited, use pushd to change the directory instead of cd; this pushes your starting directory onto a list. Using popd will then send you back to those directories, walking in reverse order (the most recent directory will be the first one retrieved with popd). The list of directories is displayed with the dirs command.
cd /tmp/dir1
pushd . Push current directoy to stack
cd /tmp/dir2
pushd . Push current directoy to stack
dirs To view directories in stack
popd To pop the top-most directory from the stack
pwd
popd To pop the top-most directory from the stack
pwd
-------------Viewing Files-----------------------------------------------------------------------------------------------
cat Used for viewing files that are not very long; it does not provide any scroll-back.
tac Used to look at a file backwards, starting with the last line.
less Used to view larger files because it is a paging program. It pauses at each screen full of text, provides scroll-back capabilities, and lets you search and navigate within the file. Note: Use / to search for a pattern in the forward direction and ? for a pattern in the backward direction. An older program named more is still used, but has fewer capabilities: "less is more".
tail Used to print the last 10 lines of a file by default. You can change the number of lines by doing -n 15 or just -15 if you wanted to look at the last 15 lines instead of the default.
head The opposite of tail; by default, it prints the first 10 lines of a file.
----------------touch------------------------------------------------------------------------------------------------------
$ touch <filename>
$ touch -t 12091600 myfile the -t option allows you to set the date and timestamp of the file to a specific value. Myfile file's timestamp to 4 p.m., December 9th (12 09 1600)
------------mkdir---------------------------------------------------------------------------------------------------------
mkdir and rmdir
mkdir sampdir It creates a sample directory named sampdir under the current directory.
mkdir /usr/sampdir It creates a sample directory called sampdir under /usr
Removing a directory is done with rmdir. The directory must be empty or the command will fail. To remove a directory and all of its contents you have to do rm -rf
------------Moving, Renaming or Removing a File---------------------------------------------------------------
mv Rename a file
rm Remove a file
rm –f Forcefully remove a file
rm –i Interactively remove a file (to prompt before every removal)
--------------Renaming or Removing a Directory-----------------------------------------------------------------
rmdir works only on empty directories; otherwise you get an error. While typing rm –rf is a fast and easy way to remove a whole filesystem tree recursively
mv Rename a directory
rmdir Remove an empty directory
rm -rf Forcefully remove a directory recursively
----------------Modifying the Command Line Prompt------------------------------------------------------------
The PS1 variable is the character string that is displayed as the prompt on the command line
user and the host system name to show up on the command line as in:
student@c8 $
The prompt above could be implemented by setting the PS1 variable to: \u@\h \$
$ echo $PS1
\$
$ PS1="\u@\h \$ "
student@c8 $ echo $PS1
\u@\h \$
student@c8 $
By convention, most systems are set up so that the root user has a pound sign (#) as their prompt
------------Standard File Streams------------------------------------------------------------------------------------
Name Symbolic Name Value Example
standard input stdin 0 keyboard
standard output stdout 1 terminal
standard error stderr 2 log file
-------------I/O Redirection--------------------------------------------------------------------------------------------
we can change its input source by using the less-than sign ( < ) followed by the name of the file to be consumed for input data:
$ do_something < input-file
If you want to send the output to a file, use the greater-than sign (>) as in:
$ do_something > output-file
Because stderr is not the same as stdout, error messages will still be seen on the terminal windows in the above example
If you want to redirect stderr to a separate file, you use stderr’s file descriptor number (2), the greater-than sign (>), followed by the name of the file you want to hold everything the running command writes to stderr:
$ do_something 2> error-file
Note: By the same logic, do_something 1> output-file is the same as do_something > output-file.
A special shorthand notation can send anything written to file descriptor 2 (stderr) to the same place as file descriptor 1 (stdout): 2>&1.
$ do_something > all-output-file 2>&1
bash permits an easier syntax for the above:
$ do_something >& all-output-file
------------Pipes----------------------------------------------------------------------------------------------------------
$ command1 | command2 | command3
The above represents what we often call a pipeline, and allows Linux to combine the actions of several commands into one.
---------------locate-------------------------------------------------------------------------------------------------------
The locate utility program performs a search taking advantage of a previously constructed database of files and directories on your system, matching all entries that contain a specified character string
$ locate zip | grep bin which will list all the files and directories with both zip and bin in their name
--------------Wildcards and Matching File Names----------------------------------------------------------------
Wildcard Result
? Matches any single character
* Matches any string of characters
[set] Matches any character in the set of characters, for example [adf] will match any occurrence of a, d, or f
[!set] Matches any character not in the set of characters
if you know only the first two letters are 'ba' of a three-letter filename with an extension of .out, type ls ba?.out
To search for files using the * wildcard, replace the unknown string with *. For example, if you remember only that the extension was .out, type ls *.out.
-------------Package Management Systems on Linux------------------------------------------------------------
Operation RPM deb
Install package rpm -i foo.rpm dpkg --install foo.deb
Install package, dependencies yum install foo apt-get install foo
Remove package rpm -e foo.rpm dpkg --remove foo.deb
Remove package, dependencies yum remove foo apt-get autoremove foo
Update package rpm -U foo.rpm dpkg --install foo.deb
Update package, dependencies yum update foo apt-get install foo
Update entire system yum update apt-get dist-upgrade
Show all installed packages rpm -qa or dpkg --list
yum list installed
Get information on package rpm -qil foo dpkg --listfiles foo
Show packages named foo yum list "foo" apt-cache search foo
Show all available packages yum list apt-cache dumpavail foo
What package is file part of? rpm -qf file dpkg --search file
---------------Process Types--------------------------------------------------------------------------------------------
Process Type Description
Interactive Processes Need to be started by a user, either at a command line or through a graphical interface such as an icon or a menu selection. bash, firefox, top
Batch Processes Automatic processes which are scheduled from and then disconnected from the terminal. These tasks are queued and work on a FIFO (First-In, First-Out) basis. updatedb, ldconfig
Daemons Server processes that run continuously. Many are launched during system startup and then wait for a user or system request indicating that their service is required. httpd, sshd, libvirtd
Threads Lightweight processes. These are tasks that run under the umbrella of a main process, sharing memory and other resources,
but are scheduled and run by the system on an individual basis. An individual thread can end without terminating the whole process and
a process can create new threads at any time. Many non-trivial programs are multi-threaded. firefox, gnome-terminal-server
Kernel Threads Kernel tasks that users neither start nor terminate and have little control over. These may perform actions like moving a thread from one CPU to another,
or making sure input/output operations to disk are completed kthreadd, migration, ksoftirqd
-------------Process and Thread IDs---------------------------------------------------------------------------------
ID Type Description
Process ID (PID) Unique Process ID number
Parent Process ID (PPID) Process (Parent) that started this process. If the parent dies, the PPID will refer to an adoptive parent; on recent kernels, this is kthreadd which has PPID=2.
Thread ID (TID) Thread ID number. This is the same as the PID for single-threaded processes. For a multi-threaded process, each thread shares the same PID, but has a unique TID.
--------Terminating a Process-----------------------------------------------------------------------------------------
To terminate a process, you can type kill -SIGKILL <pid> or kill -9 <pid>.
---------Process Priority------------------------------------------------------------------------------------------------
The priority for a process can be set by specifying a nice value, or niceness, for the process. The lower the nice value, the higher the priority. Low values are assigned to important processes, while high values are assigned to processes that can wait longer.
In Linux, a nice value of -20 represents the highest priority and +19 represents the lowest.
ps
ps lf to see priority
renice +5 3077 (id)
ps
--------------Load Averages-------------------------------------------------------------------------------------------
The load average is the average of the load number for a given period of time. It takes into account processes that are:
Actively running on a CPU
Considered runnable, but waiting for a CPU to become available
Sleeping: i.e. waiting for some kind of resource (typically, I/O) to become available.
The load average can be viewed by running w, top or uptime
-----------Interpreting Load Averages-------------------------------------------------------------------------------
The load average is displayed using three numbers (0.45, 0.17, and 0.12)
0.45: For the last minute the system has been 45% utilized on average.
0.17: For the last 5 minutes utilization has been 17%.
0.12: For the last 15 minutes utilization has been 12%.
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