Linux Tricks Tips

Introduction

serial device settings - switch off every possible hidden manipulation feature

• Output settings:

  -opost

  do not post-process output

  -onlcr

  do not translate newline to carriage return-newline

• Local settings:

  -isig

  do not enable interrupt, quit, and suspend special characters

  -icanon

  do not enable erase, kill, werase, and rprnt special characters

  -iexten

  do not enable non-POSIX special characters

  -echo

  do not echo input characters

  -echoe

  do not echo erase characters as backspace-space-backspace

  -echok

  do not echo a newline after a kill character

  -echoctl

  do not echo control characters in hat notation ('^c')

  -echoke

  kill all line by obeying the echoctl and echok setting

  19200

  sets the speed to 19200 Bit/s

Summarizing the settings prevent any additional manipulation of input or output.

usbdev - dynamic device symlink and proper access rights

Prerequisites

you have to have admin rights.

How to

• edit/create /etc/udev/rules.d/99-serial-permissions.rules
  
  • add the follwing line for general includes
    SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", SYMLINK+="$env{ID_SERIAL}", GROUP="users", MODE="0666"
    creates for every connected device of vendor id 0403 a symbolic link /dev/ to the connected device
    
  • for special devices those lines can be added in addition
    SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A100dQ2B", SYMLINK+="hadcon2", GROUP="users", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A600801P", SYMLINK+="olimex", GROUP="users", MODE="0666"
    
  • for special devices (e.g. HadCon2) those lines can be added in addition
    • SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A100*", RUN+="/usr/bin/stty -F /dev/$kernel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke 115200 "
      
    • SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A801*", RUN+="/usr/bin/stty -F /dev/$kernel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke 115200 "
      
• to find out the IDs of connected systems
  udevadm info --export-db| grep FTDI| grep ID_SERIAL
  
  
• Finally reload rules and trigger a reconnect:
  
  udevadm control --reload-rules
udevadm trigger

Links

"Writing udev rules"

http://reactivated.net/writing_udev_rules.html

udev

https://wiki.ubuntuusers.de/udev/

"Tutorial on how to write basic udev rules in Linux"

https://linuxconfig.org/tutorial-on-how-to-write-basic-udev-rules-in-linux

SSH config: Host Specific Identity

• connecting to a specific host using a different identity file and user
  
  $> cat ~/.ssh/config

     Host private.host.com
        User myname
        Hostname host.com
        IdentityFile ~/.ssh/private-identity
     Host public.host.com
        User anotherName
        Hostname host.com
        IdentityFile ~/.ssh/public-identity
     Host git.host.com
        User git
        Hostname host.com
        IdentityFile ~/.ssh/git-identity
       

• allows to replace:
  • ssh host.com -l myname -i ~/.ssh/private-identity
    by
    ssh host.com
  • commands which internally use ssh but do not allow to pass ssh options, e.g. git
    git clone git.host.com

Linux: dhclient - dynamic hostname

• Setting the System Hostname from DHCP in Ubuntu 11.10

• Automatic/Dynamic configuration of hostnames for rolling out labs

#!/bin/sh
   # Filename:     /etc/dhcp/dhclient-exit-hooks.d/hostname
   # Purpose:      Used by dhclient-script to set the hostname of the system
   #               to match the DNS information for the host as provided by
   #               DHCP.
   #
      
   # Do not update hostname for virtual machine IP assignments
   if [ "$interface" != "eth0" ] && [ "$interface" != "eth1" ] && [ "$interface" != "wlan0" ]
   then
           return
   fi
      
   if [ "$reason" != BOUND ] && [ "$reason" != RENEW ] && [ "$reason" != REBIND ] && [ "$reason" != REBOOT ]
   then
      return
   fi
   
   echo dhclient-exit-hooks.d/hostname: Dynamic IP address = $new_ip_address
   hostname=$(a=$(host $new_ip_address) || { false; } && { echo -n $a | cut -d ' ' -f 5 | cut -d "." -f 1; true; }) || unset hostname &&
   echo ${hostname?} > /etc/hostname &&
   hostname $hostname &&
   export HOSTNAME=$hostname &&
   echo dhclient-exit-hooks.d/hostname: Dynamic Hostname = $hostname

sudo curl -s https://wiki.gsi.de/pub/Epics/TipsLinuxDhclientDynamicHostname/_etc_dhcp_dhclient-exit-hooks.d_hostname -o $file && 
  sudo dos2unix $file && 
  sudo chmod a+r $file

Linux: dhclient - dynamic mount point

• Setting the System Hostname from DHCP in Ubuntu 11.10

• Automatic/Dynamic configuration of hostnames for rolling out labs

#!/bin/sh
    # Filename:     /etc/dhcp/dhclient-exit-hooks.d/mount_var_diskless
    # Purpose:      Used by dhclient-script to set mount HADES's var/diskless filesystem 
    #               from either the local net (preferred) or the GSI network
    #
    
    # Do not update hostname for virtual machine IP assignments
    if [ "$interface" != "eth0" ] && [ "$interface" != "eth1" ] && [ "$interface" != "wlan0" ]
    then
        return
    fi
    
    if [ "$reason" != BOUND ] && [ "$reason" != RENEW ] && [ "$reason" != REBIND ] && [ "$reason" != REBOOT ]
    then
            return
    fi
    
    var_diskless_hades=192.168.100.50
    var_diskless_gsi=140.181.75.158 
    var_diskless_path=/var/diskless/dreamplug
    var_diskless_mount=/var/diskless/dreamplug
    
    echo dhclient-exit-hooks.d/mount_var_diskless: new domain-name-servers: $new_domain_name_servers 
    
    echo "$new_domain_name_servers" | grep -q $var_diskless_hades && var_diskless_addr=$var_diskless_hades || var_diskless_addr=$var_diskless_gsi
    
    #clean up, but only different mounts
    grep -v "$var_diskless_addr:$var_diskless_path" /etc/mtab | grep -q "$var_diskless_mount" && umount $var_diskless_mount 
    
    #mount
    [ -d "$var_diskless_mount" ] || mkdir -p $var_diskless_mount
    grep "$var_diskless_addr:$var_diskless_path" /etc/mtab | grep -q "$var_diskless_mount" || mount $var_diskless_addr:$var_diskless_path $var_diskless_mount
    
    echo dhclient-exit-hooks.d/mount_var_diskless: mounted $var_diskless_addr:$var_diskless_path
    
    unset var_diskless_hades 
    unset var_diskless_gsi 
    unset var_diskless_path 
    unset var_diskless_mount
    

Linux: Hades Network - Allow Client To Connect Via Gateway

• with root privileges

Linux: How To Clone A SD Card

• ~/raspi.img is the location and file name of the image file.
• /dev/mmcblk0 is the SD card device on the Linux system.

Linux: Resize Raw Img File

/sbin/reboot: Input/output error

• http://www.linuxjournal.com/content/rebooting-magic-way
• http://www.buha.info/showthread.php?56521-sbin-reboot-Input-output-error

ProcServ: Remote Kill Via netcat

Solution

echo -en "\x18" | netcat -w1 localhost 12345;