I was asked this question years ago (and didnt know the answer then) and just recently I found a question and answer on Stackoverflow which basically solved this using python so I thought it would be fun to draw it out a little further.
Once you have executed chmod -x /usr/bin/chmod (or in other words you have removed executable permissions from a common tool that is used to change the permissions of files including execution) you will no longer be able to use it to make things executable including chmod.
The general answer to this question is that you need to flip the correct permission bits in order to make it executable again. chmod itself is a tool which uses underlying system calls to achieve its goal. You can also do that with other languages very easily.
NOTE I am using the
statcommand to output the file access rights in both octal (%a) and human readable (%A) format.
| command | output |
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