Shell Script that does chroot and execute commands in chroot

Question

If in shell script I write

chroot /home/mayank/chroot/codebase
cd SBC

when I run this shell script It does go in the chroot but does not execute the command cd SBC, when I exit chroot then it executes cd SBC.

How can I achieve something that does chroot and execute commands in chroot through shell script ??

try chroot /home/whatever "COMMAND" chroot can have command — Kent
– Kent, Commented Jul 12, 2018 at 12:40
chroot /home/whatever "COMMAND" I even tried that, what actually happened was, it didn't go to chroot, but executed that "COMMAND" command successfully .. — Mayank Kataruka
– Mayank Kataruka, Commented Jul 12, 2018 at 14:44
Moreover, I have many commands, that is to be run under chroot There must be some way ??? — Mayank Kataruka
– Mayank Kataruka, Commented Jul 12, 2018 at 14:52
Possible duplicate of Pass commands as input to another command (su, ssh, sh, etc) — tripleee
– tripleee, Commented Jul 13, 2018 at 8:05

Ondrej K. · Accepted Answer · 2018-07-12 20:17:52Z

24

When you run chroot without telling it what to do, it will try to start chrooted interactive shell session. So your script would "pause" at that point and when you are done with that interactive shell session, it continues out of chroot again.

One of the quick and dirt options would be to abuse here-document, like this:

chroot /home/mayank/chroot/codebase /bin/bash <<"EOT"
cd /tmp/so
ls -l
echo $$
EOT

Which takes all lines up to EOT and feeds them into bash started through chroot. Those double quotes around "EOT" should ensure bash passes the content not trying to expand variables and such. Hence that echo $$ should be PID of the inner chrooted bash.

edited Jul 12, 2018 at 20:17

answered Jul 12, 2018 at 18:19

Ondrej K.

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8 Comments

Andrey Reeshkov Over a year ago

Thereis exist way to expand some variables?

Ondrej K. Over a year ago

@AndreyReeshkov You can use <<EOT without double quotes as mentioned, but then the usual processing (parameter expansion, command substitution, arithmetic expansion) takes place in calling shell and you must escape all that is to be passed literally into the child process.

kyc1109 Over a year ago

Nice post! I also have the same problem and I also found another way with python interaction, FYI. stackoverflow.com/questions/9673730/…

n0099 Over a year ago

@AndreyReeshkov chroot MYVAR=test bash <<"EOT"\necho $MYVAR\nEOT

Ondrej K. Over a year ago

@AntonSamokat If you don't double qoute "EOT", the calling shell will already perform all the expansions... so in that example echo $$ would not be PID of the "inner" shell, but the calling one (already expanded / substituted before passing it). In that case, if one wanted to prevent such expansion, the sequence would have to be escape, e.g. in that case: echo \$\$. You can also check out the docs esp. the paragraph under the format.

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Mayank Kataruka · Accepted Answer · 2018-07-13 07:06:46Z

7

somewhat I found a solution,

chroot /work3/tmp_GU/$build_env/sbcbuild/chroot ./test.sh

after chroot giving a script there is working fine for me.

test.sh present in the chroot folder. All commands in test.sh will be executed in chroot folder.

So basically giving a command after chroot

man chroot

chroot [OPTION] NEWROOT [COMMAND [ARG]...]

answered Jul 13, 2018 at 7:06

Mayank Kataruka

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