DarshanKumar89 · February 3, 2023 12:29 · Mar 11, 2020 · Dec 4, 2019 · Oct 28, 2019 · Oct 18, 2019
diff --git a/linux.md b/linux.md
@@ -68,6 +68,10 @@ https://www.thegeekstuff.com/2011/10/grep-or-and-not-operators/
     grep 'pattern1\|pattern2' filename
     grep -E 'pattern1|pattern2' filename
 
+### Grep before after
+
+    grep -B 4 -A 4 
+
 # Locate 
 Find all instances of file
 
@@ -80,7 +84,6 @@ Find all instances of file
  * w – display who is online
  * whoami – who you are logged in as
  * finger user – display information about user
- * du – show directory space usage
  * htop - a lightweight text-mode process viewer packed with handy features such as killing processes without entering their PID, displaying full command lines, etc with a colour display
 
 ## OS Version
@@ -125,9 +128,13 @@ https://www.cyberciti.biz/faq/linux-display-date-and-time/
 
 ## Disk
 
-    df
-show disk usage
+    df -h
+
+show disk usage with human readable unit.
+
+    du -h --max-depth=1
 
+show directory space usage, only one level deep.
 ## IP
 
     ip a 
@@ -300,14 +307,21 @@ http://tldp.org/HOWTO/Bash-Prompt-HOWTO/x700.html
  * gzip -d file.gz – decompresses file.gz back to file
 
 # Process Management:
- * ps – display your currently active processes
  * top – display all running processes
  * kill pid – kill process id pid
  * killall proc – kill all processes named proc *
  * bg – lists stopped or background jobs; resume a stopped job in the background
  * fg – brings the most recent job to foreground
  * fg n – brings job n to the foreground
 
+## ps
+Display your currently active processes
+- https://unix.stackexchange.com/questions/163145/how-to-get-whole-command-line-from-a-process
+
+Show full command including arguments.
+
+    $ ps -p [PID] -o args
+
 # Network:
  * ping host – ping host and output results
  * whois domain – get whois information for domain

diff --git a/linux.md b/linux.md
@@ -24,6 +24,11 @@ Change password for user
 
     passwd user
 
+# User and group
+
+    sudo groupadd ic-api
+    sudo usermod -g ic-api ic-api
+
 # SSH 
 
 [miranda-zhang/ssh.md](https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011)
@@ -375,6 +380,6 @@ plot "frequency.dat" using 1:xticlabels(2) with boxes
 
  Create symbolic link link to file
 
-    ln -s file link
+    ln -s source_file link
 
 Without `-s`, then create hard link.
diff --git a/linux.md b/linux.md
@@ -53,13 +53,21 @@ Flags:
 
     grep -ril --include \*.py --include \*.html ".id" 
 
- * grep pattern files – search for pattern in files
-
  * command | grep pattern – search for pattern in the output of command
- * locate file – find all instances of file
 
 [More about regex](https://gist.github.com/miranda-zhang/127ff89ca8737cdb9dac404955f7f34c).
 
+### Grep OR
+https://www.thegeekstuff.com/2011/10/grep-or-and-not-operators/
+
+    grep 'pattern1\|pattern2' filename
+    grep -E 'pattern1|pattern2' filename
+
+# Locate 
+Find all instances of file
+
+    locate file
+
 # System Info:
 
  * cal – show this month's calendar

diff --git a/linux.md b/linux.md
@@ -237,7 +237,6 @@ https://gist.github.com/miranda-zhang/9871f934edbb87a23c11185b85e191be
  * cp file1 file2 – copy file1 to file2
  * cp -r dir1 dir2 – copy dir1 to dir2; create dir2 if it doesn't exist
  * mv file1 file2 – rename or move file1 to file2 if file2 is an existing directory, moves file1 into directory file2
- * ln -s file link – create symbolic link link to file
  * touch file – create or update file
  * cat > file – places standard input into file
  * more file – output the contents of file
@@ -362,3 +361,12 @@ set xtics rotate by -90
 
 plot "frequency.dat" using 1:xticlabels(2) with boxes
 ```
+
+# Symlink
+ https://shapeshed.com/unix-ln/#how-to-create-a-symbolic-link
+
+ Create symbolic link link to file
+
+    ln -s file link
+
+Without `-s`, then create hard link.
diff --git a/linux.md b/linux.md
@@ -4,15 +4,20 @@ Linux Command Cheatsheet
 # Linux Keyboard shortcuts
 open terminal: Ctrl+Alt+T
 
- * Ctrl+C – halts the current command
- * Ctrl+Z – stops the current command, resume with
+*Ctrl + C* is used to kill a process with signal SIGINT , in other words it is a polite kill .
+
+*Ctrl + Z* is used to suspend a process by sending it the signal SIGTSTP , which is like a sleep signal, that can be undone and the process can be resumed again.
+
+*Ctrl+D*: log out of current session, similar to exit.
+
+`history | grep "command looking for"`
+* Ctrl+R – type to bring up a recent command
+* !! - repeats the last command
+* exit – log out of current session
+
  * fg in the foreground or bg in the background
- * Ctrl+D – log out of current session, similar to exit
  * Ctrl+W – erases one word in the current line
  * Ctrl+U – erases the whole line
- * Ctrl+R – type to bring up a recent command
- * !! - repeats the last command
- * exit – log out of current session
 
 # Password
 Change password for user

diff --git a/linux.md b/linux.md
@@ -337,7 +337,23 @@ Possible log location
 https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sec-understanding_audit_log_files
 
 # Plot
+Graph with `gnuplot` interactively:
 
-    apt update --fix-missing
+    apt update
     apt install gnuplot-x11
-
+    gnuplot
+
+```gnuplot
+# SET TERMINAL
+set term gif
+set output 'frequency.gif'
+# set title "Word Frequency"
+
+# Axes label
+# set xlabel "Words"
+# set ylabel "Frequency"
+
+set xtics rotate by -90
+
+plot "frequency.dat" using 1:xticlabels(2) with boxes
+```
diff --git a/linux.md b/linux.md
@@ -335,3 +335,9 @@ Possible log location
     grep "denied" /var/log/audit/audit.log
 
 https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sec-understanding_audit_log_files
+
+# Plot
+
+    apt update --fix-missing
+    apt install gnuplot-x11
+
diff --git a/linux.md b/linux.md
@@ -1,4 +1,6 @@
-# Linux command cheatsheet
+Linux Command Cheatsheet
+========================
+
 # Linux Keyboard shortcuts
 open terminal: Ctrl+Alt+T
 
@@ -61,6 +63,7 @@ Flags:
  * whoami – who you are logged in as
  * finger user – display information about user
  * du – show directory space usage
+ * htop - a lightweight text-mode process viewer packed with handy features such as killing processes without entering their PID, displaying full command lines, etc with a colour display
 
 ## OS Version
 Show kernel information

diff --git a/linux.md b/linux.md
@@ -28,8 +28,13 @@ Change password for user
     find . -type f -name "*.conf"
 
 ## Grep
+Example:
+
+    grep -lr 'gceu' .
 
 `grep` pattern dir - Search for pattern in dir.
+
+Flags:
 
 `-l` (or `--files-with-matches`) option is used to only print filenames of matching files, and not the matching lines (this could also improve the speed, given that grep stop reading a file at first match with this option).
 

diff --git a/linux.md b/linux.md
@@ -90,10 +90,11 @@ Show memory and swap usage, show output in gigabytes.
     free -g
 
 ## date time
+Show the current date and time, in the format of: date+"T"+hour+minute+second+UTC time zone offset
 
-Show the current date and time
+    $ date +"%FT%H%M%S%z"
+    2019-02-19T104943+1100
 
-    date 
 https://www.cyberciti.biz/faq/linux-display-date-and-time/
 
 ## Disk

diff --git a/linux.md b/linux.md
@@ -1,5 +1,5 @@
+# Linux command cheatsheet
 # Linux Keyboard shortcuts
-
 open terminal: Ctrl+Alt+T
 
  * Ctrl+C – halts the current command
@@ -12,8 +12,7 @@ open terminal: Ctrl+Alt+T
  * !! - repeats the last command
  * exit – log out of current session
 
-# password
-
+# Password
 Change password for user
 
     passwd user

diff --git a/linux.md b/linux.md
@@ -47,6 +47,8 @@ Change password for user
  * command | grep pattern – search for pattern in the output of command
  * locate file – find all instances of file
 
+[More about regex](https://gist.github.com/miranda-zhang/127ff89ca8737cdb9dac404955f7f34c).
+
 # System Info:
 
  * cal – show this month's calendar

diff --git a/linux.md b/linux.md
@@ -304,7 +304,8 @@ CentOS
     yum install pkg
 
 Ubuntu
-
+    apt update
+    apt upgrade
     apt install pkg
 
 Node.js, Javascript package manager

diff --git a/linux.md b/linux.md
@@ -1,4 +1,4 @@
-# Keyboard shortcuts
+# Linux Keyboard shortcuts
 
 open terminal: Ctrl+Alt+T
 
@@ -12,10 +12,15 @@ open terminal: Ctrl+Alt+T
  * !! - repeats the last command
  * exit – log out of current session
 
+# password
+
+Change password for user
+
+    passwd user
+
 # SSH 
 
-miranda-zhang/ssh.md
-https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011
+[miranda-zhang/ssh.md](https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011)
 
 # Searching:
 
@@ -44,7 +49,6 @@ https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011
 
 # System Info:
 
- * date – show the current date and time
  * cal – show this month's calendar
  * uptime – show current uptime
  * w – display who is online
@@ -84,11 +88,70 @@ Show memory and swap usage, show output in gigabytes.
 
     free -g
 
+## date time
+
+Show the current date and time
+
+    date 
+https://www.cyberciti.biz/faq/linux-display-date-and-time/
+
 ## Disk
 
     df
 show disk usage
 
+## IP
+
+    ip a 
+
+One line command to just grep the ip:
+
+    ip a | grep "scope global" | grep -Po '(?<=inet )[\d.]+'
+
+For older version of centOS:
+
+    ifconfig | grep "inet " | grep -v 127.0.0.1 | awk '{print $2}'
+
+# Port and socket
+
+CentOS older
+
+`netstat`  - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
+
+`-a, --all` Show  both  listening  and  non-listening (for TCP this means established connections) sockets.  With the --interfaces option, show interfaces that are not up
+
+`--numeric , -n` Show numerical addresses instead of trying to determine symbolic host, port or user names.
+
+`-p, --program` Show the PID and name of the program to which each socket belongs.
+
+    netstat -anp | grep :8
+https://www.centos.org/docs/5/html/5.1/Deployment_Guide/s1-server-ports.html
+
+CentOS 7 netstat, which is part of the package net-tools has been officially
+**deprecated**, so you should be using `ss` (part of the package `iproute2`),
+going forward.
+
+    ss -anp | grep :8443
+
+https://unix.stackexchange.com/a/385500/36816
+
+    ss -lnpt 'sport = :3000'
+
+`-l, --listening` Display only listening sockets (omitted by default).
+
+`-n, --numeric` Do not try to resolve service names.
+
+`-p, --processes` Show process using socket.
+
+`-t, --tcp` Display TCP sockets.
+
+https://unix.stackexchange.com/questions/106561/finding-the-pid-of-the-process-using-a-specific-port
+
+# log
+
+    journalctl -u nginx.service --since today
+https://www.digitalocean.com/community/tutorials/how-to-use-journalctl-to-view-and-manipulate-systemd-logs
+
 # Environment variables
 
 [Ubuntu doc](https://help.ubuntu.com/community/EnvironmentVariables)

diff --git a/linux.md b/linux.md
@@ -50,10 +50,12 @@ https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011
  * w – display who is online
  * whoami – who you are logged in as
  * finger user – display information about user
- * uname -a – show kernel information
  * du – show directory space usage
 
 ## OS Version
+Show kernel information
+
+    uname -a
 
 Ubuntu
 
@@ -251,3 +253,11 @@ Node.js, Javascript package manager
  * ./configure
  * make
  * make install
+
+# Audit
+Possible log location
+>/var/log/audit/audit.log
+
+    grep "denied" /var/log/audit/audit.log
+
+https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sec-understanding_audit_log_files
diff --git a/linux.md b/linux.md
@@ -145,6 +145,11 @@ https://unix.stackexchange.com/a/385500/36816
 
 https://unix.stackexchange.com/questions/106561/finding-the-pid-of-the-process-using-a-specific-port
 
+# log
+
+    journalctl -u nginx.service --since today
+https://www.digitalocean.com/community/tutorials/how-to-use-journalctl-to-view-and-manipulate-systemd-logs
+
 # Environment variables
 
 [Ubuntu doc](https://help.ubuntu.com/community/EnvironmentVariables)

diff --git a/linux.md b/linux.md
@@ -12,6 +12,12 @@ open terminal: Ctrl+Alt+T
  * !! - repeats the last command
  * exit – log out of current session
 
+# password
+
+Change password for user
+
+    passwd user
+
 # SSH 
 
 [miranda-zhang/ssh.md](https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011)
@@ -104,9 +110,9 @@ For older version of centOS:
 
     ifconfig | grep "inet " | grep -v 127.0.0.1 | awk '{print $2}'
 
-# Port
+# Port and socket
 
-CentOS
+CentOS older
 
 `netstat`  - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
 
@@ -119,9 +125,23 @@ CentOS
     netstat -anp | grep :8
 https://www.centos.org/docs/5/html/5.1/Deployment_Guide/s1-server-ports.html
 
-# Socket
+CentOS 7 netstat, which is part of the package net-tools has been officially
+**deprecated**, so you should be using `ss` (part of the package `iproute2`),
+going forward.
+
+    ss -anp | grep :8443
+
+https://unix.stackexchange.com/a/385500/36816
+
+    ss -lnpt 'sport = :3000'
+
+`-l, --listening` Display only listening sockets (omitted by default).
+
+`-n, --numeric` Do not try to resolve service names.
+
+`-p, --processes` Show process using socket.
 
-    ss -lptn 'sport = :8443'
+`-t, --tcp` Display TCP sockets.
 
 https://unix.stackexchange.com/questions/106561/finding-the-pid-of-the-process-using-a-specific-port
 

diff --git a/linux.md b/linux.md
@@ -104,6 +104,27 @@ For older version of centOS:
 
     ifconfig | grep "inet " | grep -v 127.0.0.1 | awk '{print $2}'
 
+# Port
+
+CentOS
+
+`netstat`  - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
+
+`-a, --all` Show  both  listening  and  non-listening (for TCP this means established connections) sockets.  With the --interfaces option, show interfaces that are not up
+
+`--numeric , -n` Show numerical addresses instead of trying to determine symbolic host, port or user names.
+
+`-p, --program` Show the PID and name of the program to which each socket belongs.
+
+    netstat -anp | grep :8
+https://www.centos.org/docs/5/html/5.1/Deployment_Guide/s1-server-ports.html
+
+# Socket
+
+    ss -lptn 'sport = :8443'
+
+https://unix.stackexchange.com/questions/106561/finding-the-pid-of-the-process-using-a-specific-port
+
 # Environment variables
 
 [Ubuntu doc](https://help.ubuntu.com/community/EnvironmentVariables)

diff --git a/linux.md b/linux.md
@@ -43,7 +43,6 @@ open terminal: Ctrl+Alt+T
 
 # System Info:
 
- * date – show the current date and time
  * cal – show this month's calendar
  * uptime – show current uptime
  * w – display who is online
@@ -81,6 +80,13 @@ Show memory and swap usage, show output in gigabytes.
 
     free -g
 
+## date time
+
+Show the current date and time
+
+    date 
+https://www.cyberciti.biz/faq/linux-display-date-and-time/
+
 ## Disk
 
     df

diff --git a/linux.md b/linux.md
@@ -1,4 +1,4 @@
-# Keyboard shortcuts
+# Linux Keyboard shortcuts
 
 open terminal: Ctrl+Alt+T
 
@@ -14,8 +14,7 @@ open terminal: Ctrl+Alt+T
 
 # SSH 
 
-miranda-zhang/ssh.md
-https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011
+[miranda-zhang/ssh.md](https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011)
 
 # Searching:
 
@@ -87,6 +86,18 @@ Show memory and swap usage, show output in gigabytes.
     df
 show disk usage
 
+## IP
+
+    ip a 
+
+One line command to just grep the ip:
+
+    ip a | grep "scope global" | grep -Po '(?<=inet )[\d.]+'
+
+For older version of centOS:
+
+    ifconfig | grep "inet " | grep -v 127.0.0.1 | awk '{print $2}'
+
 # Environment variables
 
 [Ubuntu doc](https://help.ubuntu.com/community/EnvironmentVariables)

diff --git a/linux.md b/linux.md
@@ -12,7 +12,7 @@ open terminal: Ctrl+Alt+T
  * !! - repeats the last command
  * exit – log out of current session
 
-# SSH: 
+# SSH 
 
 miranda-zhang/ssh.md
 https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011
@@ -226,21 +226,26 @@ http://tldp.org/HOWTO/Bash-Prompt-HOWTO/x700.html
 
 # Installation:
 
+Debian
+
     dpkg -i pkg.deb
-install a package (Debian)
+
+RPM
 
     rpm -Uvh pkg.rpm
-install a package (RPM)
 
-    yum install pkg
 CentOS
 
-    apt install pkg
+    yum install pkg
+
 Ubuntu
 
-    npm install
+    apt install pkg
+
 Node.js, Javascript package manager
 
+    npm install
+
 ## Install from source:
 
  * ./configure

diff --git a/linux.md b/linux.md
@@ -207,7 +207,7 @@ http://tldp.org/HOWTO/Bash-Prompt-HOWTO/x700.html
  * gzip file – compresses file and renames it to file.gz
  * gzip -d file.gz – decompresses file.gz back to file
 
-#Process Management:
+# Process Management:
  * ps – display your currently active processes
  * top – display all running processes
  * kill pid – kill process id pid
@@ -216,19 +216,33 @@ http://tldp.org/HOWTO/Bash-Prompt-HOWTO/x700.html
  * fg – brings the most recent job to foreground
  * fg n – brings job n to the foreground
 
-##Network:
+# Network:
  * ping host – ping host and output results
  * whois domain – get whois information for domain
  * dig domain – get DNS information for domain
  * dig -x host – reverse lookup host
  * wget file – download file
  * wget -c file – continue a stopped download
 
-##Installation:
- * dpkg -i pkg.deb – install a package (Debian)
- * rpm -Uvh pkg.rpm – install a package (RPM)
+# Installation:
+
+    dpkg -i pkg.deb
+install a package (Debian)
+
+    rpm -Uvh pkg.rpm
+install a package (RPM)
+
+    yum install pkg
+CentOS
+
+    apt install pkg
+Ubuntu
+
+    npm install
+Node.js, Javascript package manager
+
+## Install from source:
 
-##Install from source:
  * ./configure
  * make
  * make install
diff --git a/linux.md b/linux.md
@@ -1 +1,234 @@
-#
+# Keyboard shortcuts
+
+open terminal: Ctrl+Alt+T
+
+ * Ctrl+C – halts the current command
+ * Ctrl+Z – stops the current command, resume with
+ * fg in the foreground or bg in the background
+ * Ctrl+D – log out of current session, similar to exit
+ * Ctrl+W – erases one word in the current line
+ * Ctrl+U – erases the whole line
+ * Ctrl+R – type to bring up a recent command
+ * !! - repeats the last command
+ * exit – log out of current session
+
+# SSH: 
+
+miranda-zhang/ssh.md
+https://gist.github.com/miranda-zhang/74a2e1c5888b69f170792a107cd67011
+
+# Searching:
+
+## Find
+
+    find . -type f -name "*.conf"
+
+## Grep
+
+`grep` pattern dir - Search for pattern in dir.
+
+`-l` (or `--files-with-matches`) option is used to only print filenames of matching files, and not the matching lines (this could also improve the speed, given that grep stop reading a file at first match with this option).
+
+`-r` recursive 
+
+`-i` ignore-case 
+
+`--include` search only files that match the file pattern  
+
+    grep -ril --include \*.py --include \*.html ".id" 
+
+ * grep pattern files – search for pattern in files
+
+ * command | grep pattern – search for pattern in the output of command
+ * locate file – find all instances of file
+
+# System Info:
+
+ * date – show the current date and time
+ * cal – show this month's calendar
+ * uptime – show current uptime
+ * w – display who is online
+ * whoami – who you are logged in as
+ * finger user – display information about user
+ * uname -a – show kernel information
+ * du – show directory space usage
+
+## OS Version
+
+Ubuntu
+
+    lsb_release -a
+
+CentOS
+
+    hostnamectl
+http://whatsmyos.com
+
+## Cpu information
+
+    cat /proc/cpuinfo
+
+Show number of cores only
+
+    grep -c ^processor /proc/cpuinfo
+
+https://stackoverflow.com/questions/6481005/how-to-obtain-the-number-of-cpus-cores-in-linux-from-the-command-line
+
+## Memory information
+
+    cat /proc/meminfo
+
+Show memory and swap usage, show output in gigabytes.
+
+    free -g
+
+## Disk
+
+    df
+show disk usage
+
+# Environment variables
+
+[Ubuntu doc](https://help.ubuntu.com/community/EnvironmentVariables)
+
+## Prints the names and values of all currently defined environment variables
+
+    printenv 
+
+## Examine the value of a particular variable
+
+    printenv DBPASS
+
+or
+
+    echo $TERM
+
+## Dollar sign
+
+The dollar sign `$` can actually be used to combine the values of environment variables in many shell commands. For example, the following command can be used to list the contents of the "Desktop" directory within the current user's home directory. 
+
+    ls $HOME/Desktop
+
+## System wide environment variables
+
+Add var into this file:
+
+    sudo -H nano /etc/environment
+
+It's important to do exact the way above, and not as the root user,
+as it may cause problems like
+[unable to login](https://askubuntu.com/questions/994127/cant-login-ubuntu-but-can-ssh-to-it). 
+If you use normal sudo to start graphical applications
+(including editors e.g. gedit), sometimes it results in the
+configuration files being owned by root,
+[read more about it here](https://askubuntu.com/questions/270006/why-should-users-never-use-normal-sudo-to-start-graphical-applications).
+
+The only time the file is read is on login, when the PAM stack is activated – specifically pam_env.so, which reads the file.
+
+Logging out and back in would apply the changes – and in fact you must do this if you want all your processes to receive the new environment. 
+[All other solutions](https://superuser.com/questions/339617/how-to-reload-etc-environment-without-rebooting)
+will only apply the environment to the single shell process, but not to anything you launch through the GUI including new terminal windows.
+
+# App info
+
+    which app
+show which app will be run by default
+
+    man command
+show the manual for command
+
+ * whereis app – show possible locations of app
+
+# Bash Shell Script
+
+`miranda-zhang/bash.md`
+https://gist.github.com/miranda-zhang/9871f934edbb87a23c11185b85e191be
+
+# File Commands:
+
+ * cd dir - change directory to dir
+ * cd – change to home
+ * pwd – show current directory
+ * mkdir dir – create a directory dir
+ * rm file – delete file
+ * rm -r dir – delete directory dir
+ * rm -f file – force remove file
+ * rm -rf dir – force remove directory dir *
+ * cp file1 file2 – copy file1 to file2
+ * cp -r dir1 dir2 – copy dir1 to dir2; create dir2 if it doesn't exist
+ * mv file1 file2 – rename or move file1 to file2 if file2 is an existing directory, moves file1 into directory file2
+ * ln -s file link – create symbolic link link to file
+ * touch file – create or update file
+ * cat > file – places standard input into file
+ * more file – output the contents of file
+ * head file – output the first 10 lines of file
+ * tail file – output the last 10 lines of file
+ * tail -f file – output the contents of file as it grows, starting with the last 10 lines 
+
+## GUI file manager
+
+    xdg-open .
+
+https://askubuntu.com/a/31196/202823
+
+## Directory listing:
+
+show hidden files with`-a`, show details with `-l`
+
+    ls -al 
+
+Determine file type, i.e. check if somthing is a symbolic link.
+
+    file
+
+Counting Files in the Current Directory
+
+    ls -1 | wc -l
+This uses wc to do a count of the number of lines (-l) in the output of ls -1. 
+http://tldp.org/HOWTO/Bash-Prompt-HOWTO/x700.html
+
+## File Permissions
+ * chmod octal file – change the permissions of file to octal, which can be found separately for user, group, and world by adding:
+ * 4 – read (r)
+ * 2 – write (w)
+ * 1 – execute (x)
+
+ Examples:
+ * chmod 777 – read, write, execute for all
+ * chmod 755 – rwx for owner, rx for group and world
+
+## Compression
+ * tar cf file.tar files – create a tar named file.tar containing files
+ * tar xf file.tar – extract the files from file.tar
+ * tar czf file.tar.gz files – create a tar with Gzip compression
+ * tar xzf file.tar.gz – extract a tar using Gzip
+ * tar cjf file.tar.bz2 – create a tar with Bzip2 compression
+ * tar xjf file.tar.bz2 – extract a tar using Bzip2
+ * gzip file – compresses file and renames it to file.gz
+ * gzip -d file.gz – decompresses file.gz back to file
+
+#Process Management:
+ * ps – display your currently active processes
+ * top – display all running processes
+ * kill pid – kill process id pid
+ * killall proc – kill all processes named proc *
+ * bg – lists stopped or background jobs; resume a stopped job in the background
+ * fg – brings the most recent job to foreground
+ * fg n – brings job n to the foreground
+
+##Network:
+ * ping host – ping host and output results
+ * whois domain – get whois information for domain
+ * dig domain – get DNS information for domain
+ * dig -x host – reverse lookup host
+ * wget file – download file
+ * wget -c file – continue a stopped download
+
+##Installation:
+ * dpkg -i pkg.deb – install a package (Debian)
+ * rpm -Uvh pkg.rpm – install a package (RPM)
+
+##Install from source:
+ * ./configure
+ * make
+ * make install
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+#