Linux/Unix misc

• Configuration file for the ls color command is /etc/DIR_COLORS for Linux
• sftp only
• ChrootDirectory: Specifies the pathname of a directory to chroot(2) to after authentication. All components of the pathname must be root-owned directories that are not writable by any other user or group. After the chroot, sshd(8) changes the working directory to the user's home directory.
• http://serverfault.com/questions/354615/allow-sftp-but-disallow-ssh
  http://serverfault.com/questions/584986/bad-ownership-or-modes-for-chroot-directory-component
• sshd_config
  

  Subsystem sftp internal-sftp
  Match group sftponly
       ChrootDirectory /home/%u
       X11Forwarding no
       AllowTcpForwarding no
       ForceCommand internal-sftp

  Or

  Match user MY_USER
    ChrootDirectory /var/www/RESTRICTED_DIR

• 
  

  # chown root:root /var/www/RESTRICTED_DIR
  # chmod 755 /var/www/RESTRICTED_DIR

• Using loop devices is very convenient when training with Raid for instance. To create usable devices for a Raid, it works as for a file-system, except that instead of mounting the file as a loop device they must be setup with the tool ”losetup” that is part of the Linux utilities. In fact, it is not possible to prepare devices for a Raid that are already mounted, and losetup makes a loop device in /dev/ ready to be mounted in a way that it is possible to run ”mount /dev/loop0 mount-point” instead of ”mount -o loop file mount-point”.
  
  Preparing a Raid5 works as follow:
  
  1. Create 3 files:
  • dd bs=1M count=100 if=/dev/zero of=0
  • dd bs=1M count=100 if=/dev/zero of=1
  • dd bs=1M count=100 if=/dev/zero of=2
  2. Setup loop devices:
  • losetup /dev/loop0 0
  • losetup /dev/loop1 1
  • losetup /dev/loop2 2
  3. Prepare the Raid5 device:
  • mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/loop0 /dev/loop1 /dev/loop2
  4. Mount the Raid5 device:
  • mount /dev/md0 mount-point
• Why VNC not showing actual Remote Desktop
• vncserver doesn't connect to the actual desktop; it creates a virtual desktop that is configured separately, on another display, probably :1. the X11 session defined in ~/.vnc/xstartup, a minimal X11 session. 
• To access a different desktop that looks the same, you have to start it in this xstartup file, e.g. with exec gnome-session or something similar, have a look for documentation on xinitrc or xsession[rc])
• To access the same desktop session, you need a different VNC server. x11vnc can dodesktop sharing; in your GNOME environment, Vino is probably the preferable choice
• you might be able to use Xvnc with inetd as described in its man page (last paragraph of the linked section). Another (kind of high-overhead but neat) solution might be using the Guacamole remote desktop gateway and configuring access there
• Please uncomment following two lines in xstartup file under ~/.vnc/xstartup:
  Before:

  #unset SESSION_MANAGER
  #exec /etc/X11/xinit/xinitrc
  
  [ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
  [ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
  xsetroot -solid grey
  vncconfig -iconic &
  xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
  twm &
  

  After:

  unset SESSION_MANAGER
  exec /etc/X11/xinit/xinitrc
  
  [ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
  [ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
  xsetroot -solid grey
  vncconfig -iconic &
  xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
  twm &

• ttt