Android Host Termux Fileserver

Android Termux Server (Server B) & Backup Fileserver

An Android smartphone repurposed as an ultra-low-power, battery-backed secondary Linux server running Termux for lightweight fileserver tasks, automated background syncing, and core DNS infrastructure.

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Server & Storage Architecture

flowchart TD subgraph AndroidOS [Android OS and Storage Subsystem] InternalStorage["Internal Storage"] MicroSD["MicroSD Card Storage"] Battery["Internal Battery UPS Backup"] end subgraph TermuxEnv [Termux Linux Userland] SSHFS["SSHFS or SFTP Server Port 8022"] Rsync["Automated Rsync Sync Engine"] Restic["Restic Encrypted Backup Agent"] end subgraph DeployedServices [Low Power Services] AdGuard["AdGuard Home DNS Port 53"] Tailscale["Tailscale Subnet Router"] Sophia["Sophia Radar Status Checks"] end Battery --> TermuxEnv InternalStorage --> TermuxEnv MicroSD --> TermuxEnv TermuxEnv --> SSHFS TermuxEnv --> Rsync TermuxEnv --> Restic TermuxEnv --> AdGuard TermuxEnv --> Tailscale TermuxEnv --> Sophia

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Storage Setup & Permissions

To allow Termux to access shared Android internal storage and external MicroSD cards:

# Request storage permission prompt in Android OS
termux-setup-storage

# Verify created storage symlinks (~/storage)
ls -la ~/storage
# dcim -> /sdcard/DCIM
# downloads -> /sdcard/Download
# shared -> /sdcard
# external-1 -> /storage/XXXX-XXXX (MicroSD)

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SFTP / SSHFS Fileserver Setup (:8022)

Termux includes OpenSSH, serving as an encrypted SFTP fileserver accessible across the Tailscale mesh:

# Install OpenSSH
pkg update && pkg install openssh -y

# Set SSH password
passwd

# Start SSH / SFTP server listening on port 8022
sshd

# Verify listening port
netstat -tlpn | grep 8022

Client SSHFS Mounting Command (From Workstation)

# Mount Termux storage onto desktop filesystem via SSHFS over Tailscale
mkdir -p ~/mnt/termux-storage
sshfs -p 8022 u0_a245@100.64.0.11:/sdcard ~/mnt/termux-storage

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Automated Remote Backup Sync Script (backup-to-server-a.sh)

Script running on Server B that periodically syncs critical phone backups and AdGuard configs to Server A (Lenovo Arch Linux):

#!/data/data/com.termux/files/usr/bin/bash
# Automated Rsync Backup from Server B (Termux) to Server A (Arch Linux)

LOG_FILE="$HOME/backup.log"
TARGET_HOST="100.64.0.10"
TARGET_DIR="/mnt/storage/backups/termux-nodes/"

echo "[$(date)] Starting sync to $TARGET_HOST..." >> "$LOG_FILE"

# Sync AdGuard Home configuration and local backups
rsync -avz -e "ssh -p 22" \
    $HOME/.adguard/ \
    terrich@$TARGET_HOST:$TARGET_DIR/adguard-backup/ >> "$LOG_FILE" 2>&1

if [ $? -eq 0 ]; then
    echo "[$(date)] Sync completed successfully." >> "$LOG_FILE"
else
    echo "[$(date)] Sync failed!" >> "$LOG_FILE"
fi