循环填充.bash_history

Question

How would one write a loop to reach the limit on $HISTFILESIZE in bash?

Something like this that would actually print the commands?

for i in $(seq 1 $HISTFILESIZE); do echo test-$i;done

The goal is to see if logs can be overwritten with a simple loop that a malicious user might use to hide his shell history. I have .bash_history append only with: chattr +a I know that relying on .bash_history is probably not the best way to keep track, this is more of a "I'm curious" question.

Thanks Jon

Answer 1

You don't need seq , Bash has two ways of providing numbers to iterate over with a for loop.

for i in {1..100}

which won't take variables as arguments (unless you use eval ).

And

for ((i = 1; i <= $HISTFILESIZE; i++))

which obviously can use variables.

You can do:

for ((i = 1; i <= $HISTFILESIZE; i++))
do
    history -s "anything you want"
done

With this technique a user can obliterate the in-memory history list of the current session. When the user exits, that list is written to the history file.

You can truncate the history file:

>~/.bash_history

Assuming it's not append-only.

Answer 2

Well, the user could always run

for i in $(seq 1 $HISTFILESIZE); do echo test-$i;done

just as you say, and paste the output into a terminal. But .bash_history is in the user's home directory, so he could chmod +w and then shred it just as easily.