A safer short note on using fsck to check Linux filesystems and why device selection matters.

chkconfig was commonly used on older Linux distributions to view and manage which services start at different runlevels. On many modern systems, systemctl has replaced it. List service settings Modern systemd equivalent Use chkconfig mainly when working with older Red Hat, CentOS or similar systems that still use the older service model.

The printenv command prints environment variables for the current shell session. These variables can affect paths, language settings, application configuration and script behaviour. Show all environment variables Show one variable This is useful when troubleshooting scripts that behave differently for different users or services.

Modern notes on shred, secure file deletion, SSD wear levelling, snapshots, encryption, and device sanitisation.

The md5sum command calculates an MD5 checksum for a file. It is useful for basic file comparison, but it should not be used for modern security-sensitive verification. Create a checksum Save and check a checksum For stronger verification, prefer SHA-256 checksums when they are available.

sum prints a simple checksum and block count for a file. It is an older utility and is mostly useful when working with legacy scripts or older Unix-style examples. Check a file For modern file verification, prefer stronger tools such as sha256sum where available.

Shell scripts are convenient, but they are a poor place to store passwords, API keys, or other long-lived secrets. Obfuscating or compiling a shell script does not provide strong secret protection because the secret must still become available to the running process. Prefer secret storage over script encryption Use a dedicated secret manager when one … Read more