My Unix Services shell is yucky – how do I change it?

You can get into Unix Services from TSO OMVS, or you can use SSH to get directly into a Unix Services session (without access to ISPF). I was interested in using SSH. At first glance it works just like a Linux command window.

My first experience was the keys did not behave as I expected, and how can I change this.

• Why do I care which shell I am using?
• How do I use a different shell?
• Your default shell
• zsh education
• Changing what keys do … getting the delete key to work as expected
• Installing useful commands
• Logon over ssh without a password.
  

Why do I care which shell I am using?

On Linux I can type the first part of a file name, press the tab key, and it either completes the name of the file (if there was only one) or lists the names of the possible matching files. This is known as autocomplete.

I tried this in an SSH session on z/OS, and this did not work. I was using the default shell, which does not have this support. I needed to use the bash shell or the zsh shell. Note the zsh was developed on Unix and ported to z/OS, it is not a z/OS special.

How do I use a different shell?

The first question is, “is the shell available on my system?”, to which the answer is maybe.

• z/OS ships with the default shell in /bin/sh.
• You can get a free version of bash for z/OS. My ADCD based system does not have Bash pre-installed. I believe you can get it for free from Rocket.
• My ADCD system has zsh installed (but not configured).

Your default shell

This is set in the in your RACF OMVS segment PROGRAM field . To display it, use

TSO LU COLIN OMVS

This gave me

OMVS INFORMATION
----------------
UID= 0000990021
HOME= /u/colin
PROGRAM= /bin/sh
...

Once you logon to your shell various profiles may be executed if they exist for example for the default shell

• /etc/profile and ~/.profile where ~ is your default home directory (see HOME= in the output of the LU command, above;

Typically the profile script will set the environment variable SHELL.
I put the following in my ~/.profile so my SSH sessions get the zsh shell.

#!/bin/sh 

if [[ -z "$SSH_CLIENT"  ]] 
  then 
    # dummy 
    xxx="$SSH_CLIENT" 
  else 
    # SSH_CLIENT has a value ...  so an SSH terminal 
     #cho "using the zsh shell" 
     zsh="/bin/zsh" 
     echo "shell  $SHELL zsh  $zsh" 
     if [[ $SHELL != $zsh ]] 
       then 
         echo "using the zsh shell" 
         export SHELL="$zsh" 
         exec "$zsh" 
    fi 
fi 

zsh is documented in the UNIX System Services Command Reference. This is a big book, so I extracted the section of zsh using

pdftk USSCommand_v3r1.pdf cat 899-1071 output zsh.pdf

zsh education

I found https://thevaluable.dev/zsh-completion-guide-examples/ was a good source of information about zsh.

If zsh has been installed properly you should have an environment variable $ZDOTDIR defined. If this is missing then $HOME is used instead.

There are files

• $ZDOTDIR/.zshenv
• $ZDOTDIR/.zprofile
• $ZDOTDIR/.zshrc
• $ZDOTDIR/.zlogin
• $ZDOTDIR/.zlogout

Which should contain configuration information

There are comment on the IBM community about the poor documention of zsh on z/OS, an how you can get started. It gives hints on setting up colours etc.

The IBM documentation says

• Commands are first read from /etc/zshenv; this cannot be overridden. …
• Commands are then read from $ZDOTDIR/.zshenv.
  • If the shell is a login shell, commands are read from /etc/zprofile and then $ZDOTDIR/.zprofile.
  • Then, if the shell is interactive, commands are read from /etc/zshrc and then $ZDOTDIR/.zshrc.
  • Finally, if the shell is a login shell, /etc/zlogin and $ZDOTDIR/.zlogin are read.
• When a login shell exits, the files $ZDOTDIR/.zlogout and then /etc/zlogout are read. This happens with either an explicit exit via the exit or logout commands, or an implicit exit by reading end-of-file from the terminal

If you start with the system shell, then invoke the zsf shell, the PATH and LIBPATH statements etc will be inherited from the system shell.
If you go directly to the zsh you’ll need to set up a profile based on the system profile. ( or just invoke the existing profile).

You may want to set up a profile to set the command prompt for example the default is

$LOGNAME:$PWD:

You can set it with

export prompt='%n:%/'

to give

COLIN:/u/colin

Changing what keys do … getting the delete key to work as expected

This took a while to understand see Linux mapping the keyboard and on z/OS SSH.

Installing useful commands

I installed zopen. zopen provides lots of Unix-like packages on z/OS. Its home page says

The zopen community is here to provide popular Open Source tools and to encourage z/OS Open Source tools development. We currently host 200+ z/OS Open Source projects and we’re looking for more!

See installing zopen. I then installed the less command , and openssl. See installing packages.