Linux Tips

Terminator (Terminal)

Securing SSH Public/Private Keys with Password

kkr@host341:~$ eval $(ssh-agent)
Agent pid 31015
kkr@host341:~$ ssh-add
Enter passphrase for /home/kkr/.ssh/id_rsa: **********************
Identity added: /home/kkr/.ssh/id_rsa (/home/kkr/.ssh/id_rsa)
kkr@host341:~$ 

Using Screen

To remove a session, login with screen -x NAME and type in quit or press CTRL+d.

Fix Scrolling in Screen

Adding the following lines to the ~/.screenrc fixes the scroll-problem with the mouse or SHIFT + PAGE_UP:

termcapinfo xterm* ti@:te@

Fix Promt in Screen

echo 'shell -/bin/bash' > ~/.screenrc

VNC Viewer

Pressing F8 + F (to switch to full-screen mode) allows you to pass all system keys (e.g. CTRL + ALT + ARROWs) to the remote system. With F8 + Z you can minimize the viewer - and open it again with ALT + TAB.

Start Server

$ vncserver -localhost no

Access without Password

$ mkdir -p .vnc
$ scp 10.10.60.120:.vnc/passwd .vnc/passwd_10.10.60.120
$ chmod 600 .vnc/passwd_10.10.60.120
$ vncviewer --PasswordFile=.vnc/passwd_10.10.60.120  10.10.60.120:1

Update Alternatives

$ update-alternatives --get-selections
Xvnc                           auto     /usr/bin/Xtigervnc
animate                        auto     /usr/bin/animate-im6.q16
animate-im6                    auto     /usr/bin/animate-im6.q16
aptitude                       auto     /usr/bin/aptitude-curses
automake                       auto     /usr/bin/automake-1.15
awk                            auto     /usr/bin/gawk
builtins.7.gz                  auto     /usr/share/man/man7/bash-builtins.7.gz
c++                            auto     /usr/bin/g++
...
$

$ sudo update-alternatives --config gcc
There are 2 choices for the alternative gcc (providing /usr/bin/gcc).

  Selection    Path              Priority   Status
------------------------------------------------------------
* 0            /usr/bin/gcc-4.9   20        auto mode
  1            /usr/bin/gcc-4.9   20        manual mode
  2            /usr/bin/gcc-6     10        manual mode

Press <enter> to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/bin/gcc-6 to provide /usr/bin/gcc (gcc) in manual mode
$

Disable Host-Key Checking

$ ssh -p20160 root@10.20.60.203
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:XvRoOq+r9mRiWavIIWVhX52qYLEKCoeH83fa8O4TUvM.
Please contact your system administrator.
Add correct host key in /home/kkr/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /home/kkr/.ssh/known_hosts:222
  remove with:
  ssh-keygen -f "/home/kkr/.ssh/known_hosts" -R [10.20.60.203]:20160
ECDSA host key for [10.20.60.203]:20160 has changed and you have requested strict checking.
Host key verification failed.
$

Host 10.0.*
	StrictHostKeyChecking no
	UserKnownHostsFile=/dev/null
	LogLevel ERROR
Host 10.20.60.*
	StrictHostKeyChecking no
	UserKnownHostsFile=/dev/null
	LogLevel ERROR

Share Bash History from multiple Terminals

# Avoid duplicates
HISTCONTROL=ignoredups:erasedups  
# When the shell exits, append to the history file instead of overwriting it
shopt -s histappend

# After each command, append to the history file and reread it
PROMPT_COMMAND="${PROMPT_COMMAND:+$PROMPT_COMMAND$'\n'}history -a; history -c; history -r"

XZ Compression

• Using xz [FILE] for compressing [FILE] to [FILE].xz ([FILE] will be removed)
• Using xz -k [FILE] for compressing [FILE] to [FILE].xz ([FILE] will be not removed)
• Using unxz [FILE].xz for decompressing [FILE].xz to [FILE] ([FILE].xz will be removed)
• Using tar cJ [FILE].xz [FOLDER] for compressing folders
• Using xv --threads=0 [FILE] for compressing with threads

Grep

• Using --color to highlight matches
• Using -I to exclude binary matches
• Using -o to show only matches
• Using -v to show only what _not_ matches

Nice

$ nice -5 bitbake --read=extra.conf mrt.base.linux
[...]
$

$ sudo nice --5 sleep 2
[...]
$

Find

find var/log/ -iname "anaconda.*" -exec tar -rvf file.tar {} '+'

find . -name "*.sh" -exec sed -i 's/#! \?\/bin\/sh/#!\/bin\/bash/' {} \;

find . -name "2018-*" -print0 | xargs -0 ~/Dropbox/Pictures/Tools/rename_dropboximage_to_mobile.sh

>./2018-11-06 17.50.36.jpg<
>./2018-11-01 11.48.37.jpg<
>./2018-11-07 21.51.18.jpg<
>./2018-11-01 20.57.13.jpg<
>./2018-11-06 16.37.25.jpg<

DIR=$(realpath $1)
LOG=$DIR/hash_list.txt

find $DIR -not -type d -print0 | while IFS='' read -r -d '' FILE; do 
	echo -n "Check '$FILE': "
	if grep -q "$FILE" $LOG ; then
		echo "already in list"
	else
		md5sum "$FILE" | tee -a "$LOG"
	fi
done

XFCE Shortcuts

Installation Proposal

$ ITGSend
The program 'ITGSend' is currently not installed.  You can install it by typing:
apt install d-itg
ITGSend: command not found
$

$ dislay

Command 'dislay' not found, did you mean:

  command 'display' from deb graphicsmagick-imagemagick-compat

Try: sudo apt install <deb name>

$

One reason for a crash of the command-not-found tool is a wrong encoding:

$ dislay
Sorry, command-not-found has crashed! Please file a bug report at:
http://www.debian.org/Bugs/Reporting
Please include the following information with the report:

command-not-found version: 0.3
Python version: 3.7.3 final 0
Distributor ID:	Debian
Description:	Debian GNU/Linux 10 (buster)
Release:	10
Codename:	buster
Exception information:

unable to open database file
Traceback (most recent call last):
  File "/usr/share/command-not-found/CommandNotFound/util.py", line 23, in crash_guard
    callback()
  File "/usr/lib/command-not-found", line 90, in main
    cnf = CommandNotFound.CommandNotFound(options.data_dir, do_raise=True)
  File "/usr/share/command-not-found/CommandNotFound/CommandNotFound.py", line 86, in __init__
    self.db = SqliteDatabase(dbpath)
  File "/usr/share/command-not-found/CommandNotFound/db/db.py", line 12, in __init__
    self.con = sqlite3.connect(filename)
sqlite3.OperationalError: unable to open database file

This can be fixed by setting the locale to UTF-8 in the .bashrc:

export LANGUAGE=en_US.UTF-8
export LANG=en_US.UTF-8
export LC_ALL=en_US.UTF-8

and recreate your system locals:

$ sudo locale-gen en_US.UTF-8
$ sudo dpkg-reconfigure locales

SSH Connection Check (on Server)

if [ -n "$SSH_CONNECTION" ] ; then
	if [ "$(readlink /proc/$$/fd/0)" != "/dev/null" ] ; then
		echo
		echo "The update does fail when it is started via SSH (since the network"
		echo "and the sshd will be shut down)."
		echo
		echo "Please trigger script by software (e.g. via web-browser), start it"
		echo "on the serial console or via SSH with"
		echo
		echo "   nohup /usr/bin/flashupdate &"
		echo
		sleep 10
		exit 1
	fi
fi

VNC Sessions

There is only one pitfall on Linux/Debian - you have to start the serve with -localhost no, otherwise it binds only on the loopback device and is not reachble from outside.

$ vncserver -alwaysshared -localhost no

Password File

$ scp $REMOTEIP:.vnc/passwd ~/.vnc/passwd_$REMOTEIP
password: ****
$ vncviewer --PasswordFile=$HOME/.vnc/passwd_$REMOTEIP $REMOTEIP:1

Shortcuts

The repository '...' does not have a Release file

$ sudo apt-get update
[...]
Reading package lists... Done                      
E: The repository 'http://ppa.launchpad.net/octave/stable/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
$

deb [trusted=yes] http://ppa.launchpad.net/octave/stable/ubuntu bionic main
# deb-src http://ppa.launchpad.net/octave/stable/ubuntu bionic main