Linux & Shell Operations

Essential operational runbook for Linux shell workflows, terminal multiplexing, cryptographic operations, networking diagnostics, and API testing.

Terminal Multiplexing (Tmux)

Navigate scrollback buffers and copy terminal output in tmux:

• Ctrl-b [ : Enter scroll/copy mode.
• Use standard Vim motion keys (h, j, k, l, Ctrl-u, Ctrl-d) to scroll through history.
• Space : Begin text selection.
• Enter : Copy selection to tmux clipboard buffer.
• q : Exit scroll/copy mode and return to prompt.

Cryptography & Key Management

Ed25519 SSH Keypair Generation

Generate high-security Ed25519 SSH keys with explicit comments and path specifications:

ssh-keygen -t ed25519 -C "przemek@sagalo.pro" -f ~/.ssh/id_ed25519_custom

Binary MD5 Digest (Base64 Encoded)

Calculate the base64-encoded binary MD5 hash of a file (frequently used for AWS S3 Content-MD5 integrity checks):

openssl dgst -md5 -binary filename.tar.gz | openssl base64

Networking & Filesystem Tools

CIDR Subnet Calculation (ipcalc)

Calculate network boundaries, broadcast addresses, and usable host counts from CIDR notation:

ipcalc 192.168.1.0/24

Directory Tree Visualization

Display directory hierarchies in a tree structure:

# Display 2 levels deep including hidden directories
tree -L 2 -a

# Ignore specific build/cache directories
tree -I ".git|node_modules|__pycache__|.venv"

Stream Editing (sed)

Quick regex-based stream replacement:

# In-place substitution
sed -i 's/search_pattern/replacement_text/g' path/to/file.txt

API Testing & Token Authentication (cURL)

1. OAuth2 Client Credentials Flow

Retrieve an OAuth2 bearer access token from a secure token endpoint using client credentials:

curl --location --request POST "https://auth.example.com/oauth2/token" \
  --header "Content-Type: application/x-www-form-urlencoded" \
  --data-urlencode "grant_type=client_credentials" \
  --data-urlencode "client_id=<CLIENT_ID>" \
  --data-urlencode "client_secret=<CLIENT_SECRET>"

2. Authenticated API Request

Invoke a REST endpoint using the retrieved Bearer token:

curl --request GET "https://api.example.com/prod/resource" \
  --header "Authorization: Bearer <ACCESS_TOKEN>" \
  --header "Accept: application/json"

HTTP Request Types & Idempotency

Understanding standard HTTP verb semantics and idempotency guarantees: