Shell – How to enable ksh command history between sessions

command historykshmkshshell

If I start ksh or mksh, my upwards arrow does nothing:

$ ksh
$ ^[[A^[[A^[[A^[[A^[[A

But it works with bash if I start bash and press the upwards arrow.

$ bash
developer@1604:~$ ssh root@127.0.1.2 -p 2223

I have no history if I start ksh or mksh. I even set the $HISTFILE variable and still no history if I start a new shell.

What can I do about it? Is it true that the Korn shell can't remember history between sessions while the bash shell can?

If I like the Korn shell and I want a better and more extensive history, is it possible to use that functionality with ksh?

Best Answer

No, this is not true.

If $HISTFILE is a filename, then the session history will be stored in that file. This is explained in the manual. The number of commands remembered in the shell history is limited by the value of $HISTSIZE.

I believe that the history is flushed to the file after the execution of each command, as opposed to bash that flushes the history to file when the shell session ends. This may depend on which implementation of ksh you are using.

Set HISTFILE to a filename in your ~/.profile file (which is read by login shells), or in the file pointed to by $ENV (which is read by interactive shells and has the default value of $HOME/.kshrc in ksh93). $HISTSIZE is by default 500 or 512 or something thereabouts depending on the implementation of ksh you are using. Neither of these variables need to be exported. The history file does not need to exist before doing this.

In comments you mention that some Emacs movement and command line editing keys do not work. This is because the shell is not in Emacs editing mode. Either set the variable EDITOR (or VISUAL) to emacs or use set -o emacs to enable Emacs command line editing mode. This is also explained in the manual. These variable also do not need to be exported unless you want other programs than the shell to use them.

Summary:

In your $HOME/.profile file:

export ENV="$HOME/.kshrc"

In your $HOME/.kshrc file:

HISTFILE="$HOME/.ksh_history"
HISTSIZE=5000

export VISUAL="emacs"
export EDITOR="$VISUAL"
set -o emacs

This has been thoroughly tested on OpenBSD with both ksh93 and pdksh (which is ksh on OpenBSD). I don't use mksh, but since it's a pdksh derivative, I believe this would work with that shell too.

Note that pdksh and ksh93 (and bash) can not share history file as they have different history formats.

This is usually not a problem if you have separated initialization files for bash and ksh, e.g. .bash_profile and .bashrc for bash and .profile and .kshrc for ksh (with export ENV="$HOME/.kshrc" in .profile). You may further distinguish various ksh implementations by looking at $KSH_VERSION (usually).

Related Solutions

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:

Zsh – HISTFILE Still Reads from ~/.zsh_history

Setting HISTFILE in your zsh configuration really should change to where the history is written and from where it is read. It is likely that oh-my-zsh sets HISTFILE=~/.zsh_history before you set it, in which case the history has already been read from ~/.zsh_history.

Looking at the oh-my-zsh code, there are two ways to solve this:

set HISTFILE before loading oh-my-zsh. That is, it has to be set in your ~/.zshrc before the line containing
```
source $ZSH/oh-my-zsh.sh
```
This would be a simple solution, if you only want to change HISTFILE.
overload the history.zsh module with your own custom version. Oh-my-zsh loads all files matching $ZSH/lib/*.zsh (where $ZSH usually is ~/.oh-my-zsh) at startup, unless in ${ZSH_CUSTOM}/lib/ is a file with the same name (ZSH_CUSTOM usually is $ZSH/custom). The history settings can be found in $ZSH/lib/history.zsh and can therefore replaced by ${ZSH_CUSTOM}/lib/history.zsh.

If you want to change more of the settings found in $ZSH/lib/history.zsh this is probably the way to go. Otherwise you would have to set HISTFILE before loading oh-my-zsh and everything else after.

A way to change HISTFILE (temporarily) later in a shell session is

fc -p /path/to/new_history

This puts the current history on a stack, sets HISTFILE=/path/to/new_history and reads the history from that file (if it exists). Any new commands will then also be written to the new HISTFILE. You can go back to the original history with fc -P.

Best Answer

Related Solutions

Bash – Shell – Deal with multiple command history files

Zsh – HISTFILE Still Reads from ~/.zsh_history

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