Category: system admin

Hide commands from bash history temporarily

There’s been a number of times I’ve wanted to not include some commands that I type into bash from being added to bash_history

The most convenient is to start a subshell by typing in bash again. This ensures that the commands in the subshell don’t get added to the history.

There are additional ways of achieving this as well.

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mesg: ttyname failed: Inappropriate ioctl for device

While running a cron job in Linux, I sometimes get this error and I had been struggling to solve this until I came across this post.

Although that particular post mentions the cause being Vagrant, mine was due to a cron job.

First the solution …

Modify .profile under home folder

Open ~/.profile

Replace the following line –

mesg n || true

with

tty -s && mesg n

The reason for this is given very well in the post linked above.

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Postgres DB migration error due to replication

We got a weird error today when running the latest migration on a production Postgres DB.

cannot update table "schema_info" because it does not have a replica identity and publishes updates

The table schema_info is created when we run ruby Sequel migrations. This table stores just the version number of the latest migration applied under a column called version.

We had set up a replica database some time ago and it looked like the issue was because of this.

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Disable specific default Windows key shortcuts

A number of times, I prefer to use the Windows key on the keyboard to create shortcuts, especially to applications which I use frequently.

However, Windows has a default set of keyboard shortcuts that it maps to various applications and those key mappings can’t be changed. A few examples are Cortana (Win+C), Clipboard (Win+V).

To get around this, the Registry Editor needs to be modified.

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users and sudo in Linux

Every time I need to create, modify, grant sudo access to users in Linux, I have to search for it.

This is a list of the commands I’ve used in the past.

Will keep updating this so that I don’t have to load a search page every time!

All commands below are run as root user. If I’m not the root user, I need to prefix them with sudo!

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Create Postgres replica on separate server over the network

A database replica is able to provide another layer of protection in case of the main database server going down.

Postgres has this capability out of the box.

In this case the requirement was to create a replica on a separate server. (It’s also possible to create it on the same server where Postgres is running).

The replica maintains an exact copy of the main database (called Primary) on a real-time basis.

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Run Postgres exposed to the internet

Although this is not recommended, there might be scenarios where there are no other options.

An example is an analysis software which doesn’t give the capability to connect via SSH. I came across this scenario when someone wanted to use QLik. Although this has a lot of capabilities, but when something like this is required, I’d rather use the open source and free Metabase.

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