# sudo apt-get install --reinstall bash

sudo: unable to resolve host ubuntu
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded.
Need to get 643 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://mo.archive.ubuntu.com/ubuntu/ saucy/main bash amd64 4.2-5ubuntu3 [643 kB]
Fetched 643 kB in 3s (179 kB/s)
(Reading database ... 250072 files and directories currently installed.)
Preparing to replace bash 4.2-5ubuntu3 (using .../bash_4.2-5ubuntu3_amd64.deb) ...
dpkg (subprocess): unable to execute old pre-removal script (/var/lib/dpkg/info/bash.prerm): Permission denied
dpkg: warning: subprocess old pre-removal script returned error exit status 2
dpkg: trying script from the new package instead ...
dpkg (subprocess): unable to execute new pre-removal script (/var/lib/dpkg/tmp.ci/prerm): Permission denied
dpkg: error processing /var/cache/apt/archives/bash_4.2-5ubuntu3_amd64.deb (--unpack):
 subprocess new pre-removal script returned error exit status 2
/bin/df: ‘/run/user’: No such file or directory
                                               /bin/df: ‘/sys/fs/cgroup/systemd’: No such file or directory
                                                                                                           dpkg (subprocess): unable to execute installed post-installation script (/var/lib/dpkg/info/bash.postinst): Permission denied
dpkg: error while cleaning up:
 subprocess installed post-installation script returned error exit status 2
Errors were encountered while processing:
 /var/cache/apt/archives/bash_4.2-5ubuntu3_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)