Bash – How to sync terminal session command history in bash

bashcommand historysynchronization

I've
tried to search in ~/.bash_history for my recent commands while in a
terminal session but they just weren't there. I guess this is because I
have multiple terminal sessions open.

Is there a way that I can sync (ie. sync-push or sync-write-out) the
current terminal session's command history into the bash_history file
(without closing the session and losing that environment)?

(It would be remotely similar in idea to how the sync command stores
the file-system modifications on some systems.)

I imagine I could set up bash to preserve multiple session history but
the ability to push the current history buffer would still be useful in
scenarios when you are working on a new machine and you accidentally
forgot to set up bash the way you may would have wanted.

Best Answer

Add this line to .bashrc:

export PROMPT_COMMAND="history -a; history -n"

Open new terminal and check.

Explanation

history -a appends new history lines to history file.
history -n tells bash to read lines that is not read from history file to current history list of session.
PROMPT_COMMAND: contents of this variable is run as regular command before bash show prompt. So every time after you execute a command, history -a; history -n is executed, and your bash history is synced.

Related Solutions

Bash – Programmatically Add Entries to Bash History with Proper Timestamps

I posted this question on the help-bash mailing list and got a response from Chet Ramey, the maintainer of Bash.

He suggested adding either of the following before the history -s command:

set -H    # aka set -o histexpand

histchars='!^#'

I tried each of them and they both work. The reason is that the history comment character which defaults to # hasn't been set at the point that the profile code is running and so is null (\0).

Here's my working file:

HISTTIMEFORMAT='%c : '
histchars='!^#'
set -o history
history -s "# some text as a marker"

Bash – Shell – Deal with multiple command history files

Shell history files are a poor way of auditing commands. They can trivially be modified or bypassed by users. They are only useful if you trust users not to deliberately or accidentally bypass the auditing mechanism. For example, commands started from a GUI, from an editor, etc. aren't recorded this way. There are many other ways a user could launch non-logged commands and even maintain plausible deniability that they were doing it for convenience or without realizing it and not as a deliberate attempt to bypass a security measure.

If you make the history files append-only (which requires running chattr +a as root on the history file), then everything that's been recorded stays recorded, but it's still easy to bypass the recording.

Rather than keep separate history files, you could keep a single history file and back it up regularly. That will retain the date at which commands were executed, but not the terminal.

If you need to have some confidence that the logs correspond to the commands that were executed, shell history files are the wrong tool. Use the audit daemon instead. Configure it to log all execve calls.

auditctl -A exit,always -S execve

See the following questions for more information:

Best Answer

Related Solutions

Bash – Programmatically Add Entries to Bash History with Proper Timestamps

Bash – Shell – Deal with multiple command history files

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