Relatively often I have to run some command every n seconds, to see what is happening.
To do this I generally resort to writing simple one liner in shell:
=$ while true; do some command; sleep 5; done
Tag: bash
How to get advisory lock in shell?
Recently we had interesting problem. There are some maintenance tools, that do stuff that touch database. One can be calling repack, another can be specific dump, and yet another can be applying migrations from application.
The problem is that they can step over each other toes, and cause issues.
So we needed to add some way to prevent them from running at the same time…
Reconnecting to SSH servers
In my work I'm often in situation where I want to restart remote server, and then immediately connect to it over ssh.
This can be done by repeating ssh HOST in shell, but it gets tedious.
How to efficiently dump PostgreSQL databases
Recently, on irc, there have been some talks with people using various pg_dump/pg_dumpall calls to get dumps of database.
I voiced my ideas, but figured it could be good subject for a blog post.
Continue reading How to efficiently dump PostgreSQL databases
How to run short ALTER TABLE without long locking concurrent queries
Recently I've seen case like:
- application had to add column to table.
- application ran ALTER TABLE ADD COLUMN (without default!)
- everything stopped for many MINUTES
Why? How to avoid the problem?
Continue reading How to run short ALTER TABLE without long locking concurrent queries
New shell_util to watch output in multiple tmux panes at once
I assume most of you are familiar with watch program. If not – it shows, periodically, output of a command.
I was missing similar functionality for tmux, especially when I have multiple windows/panes.
So I wrote tmux_watch_many.
How to use it?
Continue reading New shell_util to watch output in multiple tmux panes at once
Wait for program(s) in tmux panes to end…
I am doing quite a lot of work inside tmux. I especially love that I can start multiple windows/panes and use them to run the same thing across multiple servers, while still having normal shell access between steps.
This thing was greatly improved when I wrote tmux_send_to_many, but one thing was missing – waiting for the thing, running in tmux window to end.
Generally, I had to look at all the windows, and decide when to launch next step on my own.
Not anymore.
visual sleep in shell, and shell_utils repo information
I wrote previously about tmux_send_to_many and group_by shell tools that I authored.
Since then I got some more ideas for changes, and for new tool, so figured I'll make an honest git repo for it. Repo is on GitLab, and all the tools inside can be freely used.
While I was doing it, I fixed some things in tmux_send_to_many.
And then – I remembered that for long time I was missing “visual-sleep" type of tool. One that will show some progress information while it's working.
Enter vsleep.
Continue reading visual sleep in shell, and shell_utils repo information
Grouping values in shell
I assume that everyone reading my blog understands GROUP BY clause in SQL.
Lately I've been doing some maintenance work, and found myself in a position that I could really use similar thing in shell.
Automation for doing stuff in multiple windows in tmux
Tmux is terminal multiplexer. Kinda like old screen, but with much more functionality.
When I work on my servers, it's pretty common that I have to do the same things to multiple servers. To make my life easier I start tmux, and in there start many “windows", each related to work on single server.
I name the windows in a way that let's me quickly find them, without false positives.
For example, if I'd have to upgrade servers db1..db5 then I'd create windows “up-db1" .. “up-db5", and each window would work on single server.
This is already scriptable – let's assume I'd want to show uptime in all of the windows, I can:
tmux lsw -F '#W' | grep -E '^up-db[0-9]+$' | xargs -r -d$'\n' -I% tmux send-keys -t % uptime Enter
But this gets tedious fast.
Continue reading Automation for doing stuff in multiple windows in tmux