Chapter 21. Restricted Shells

Disabled commands in restricted shells

. Running a script or portion of a script in restricted mode disables certain commands that would otherwise be available. This is a security measure intended to limit the privileges of the script user and to minimize possible damage from running the script.

The following commands and actions are disabled:


Example 21-1. Running a script in restricted mode

   1 #!/bin/bash
   2 
   3 #  Starting the script with "#!/bin/bash -r"
   4 #+ runs entire script in restricted mode.
   5 
   6 echo
   7 
   8 echo "Changing directory."
   9 cd /usr/local
  10 echo "Now in `pwd`"
  11 echo "Coming back home."
  12 cd
  13 echo "Now in `pwd`"
  14 echo
  15 
  16 # Everything up to here in normal, unrestricted mode.
  17 
  18 set -r
  19 # set --restricted    has same effect.
  20 echo "==> Now in restricted mode. <=="
  21 
  22 echo
  23 echo
  24 
  25 echo "Attempting directory change in restricted mode."
  26 cd ..
  27 echo "Still in `pwd`"
  28 
  29 echo
  30 echo
  31 
  32 echo "\$SHELL = $SHELL"
  33 echo "Attempting to change shell in restricted mode."
  34 SHELL="/bin/ash"
  35 echo
  36 echo "\$SHELL= $SHELL"
  37 
  38 echo
  39 echo
  40 
  41 echo "Attempting to redirect output in restricted mode."
  42 ls -l /usr/bin > bin.files
  43 ls -l bin.files    # Try to list attempted file creation effort.
  44 
  45 echo
  46 
  47 exit 0

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