Below is a complete script for backing up MSSQL Server databases on Linux, with Telegram notifications included (you can remove the Telegram part if not needed).

#!/bin/bash

# Configuration
SERVER="localhost"                            # SQL Server address
USERNAME="sa"                                # SQL Server username
PASSWORD="your_secure_password"               # SQL Server password
BACKUP_PATH="/backup/mssql/$(date +%F)"      # Backup directory (e.g., /backup/mssql/YYYY-MM-DD)
RETENTION_DAYS=7                             # Days to keep backups
TELEGRAM_BOT_TOKEN="your_bot_token"          # Telegram bot token (optional)
TELEGRAM_CHAT_ID="your_chat_id"              # Telegram chat ID (optional)
LOG_FILE="/var/log/mssql_backup.log"         # Log file for backup process

# Function to log messages
log_message() {
  echo "$(date '+%Y-%m-%d %H:%M:%S') - $1" | tee -a "$LOG_FILE"
}

# Create backup directory
if [ ! -d "$BACKUP_PATH" ]; then
  mkdir -p "$BACKUP_PATH"
  chmod 755 "$BACKUP_PATH"
  chown mssql:mssql "$BACKUP_PATH"  # Adjust user:group as needed
  if [ $? -ne 0 ]; then
    log_message "ERROR: Failed to create backup directory $BACKUP_PATH"
    exit 1
  fi
fi

# Get list of databases
DATABASES=$(sqlcmd -S "$SERVER" -U "$USERNAME" -P "$PASSWORD" -Q "SET NOCOUNT ON; SELECT name FROM sys.databases WHERE name NOT IN ('master', 'tempdb', 'model', 'msdb');" -h -1 -W)
if [ -z "$DATABASES" ]; then
  log_message "ERROR: No databases found to back up."
  exit 1
fi

# Count total databases
TOTAL_DBS=$(echo "$DATABASES" | wc -l)
SUCCESS_DBS=0
log_message "Found $TOTAL_DBS databases to back up."

# Loop through each database
for DATABASE in $DATABASES; do
  if [ -n "$DATABASE" ]; then
    BACKUP_FILE="$BACKUP_PATH/${DATABASE}_backup_$(date +%F_%H%M%S).bak"
    log_message "Backing up database $DATABASE to $BACKUP_FILE..."

    # Perform backup
    sqlcmd -S "$SERVER" -U "$USERNAME" -P "$PASSWORD" -Q "BACKUP DATABASE [$DATABASE] TO DISK = N'$BACKUP_FILE' WITH INIT, NAME = 'Full Backup of $DATABASE'"
    if [ $? -eq 0 ]; then
      log_message "Backup of $DATABASE successful."
      ((SUCCESS_DBS++))

      # Compress backup file
      BACKUP_ZIP="${BACKUP_FILE}.gz"
      if gzip -c "$BACKUP_FILE" > "$BACKUP_ZIP"; then
        rm -f "$BACKUP_FILE"
        log_message "Compressed backup to $BACKUP_ZIP"
      else
        log_message "ERROR: Failed to compress $BACKUP_FILE"
      fi
    else
      log_message "ERROR: Backup of $DATABASE failed."
    fi
  fi
done

# Clean up old backups
log_message "Cleaning up backups older than $RETENTION_DAYS days..."
find /backup/mssql/ -maxdepth 1 -type d -mtime +"$RETENTION_DAYS" -exec rm -rf {} \;
if [ $? -eq 0 ]; then
  log_message "Old backups cleaned successfully."
else
  log_message "ERROR: Failed to clean old backups."
fi

# Send Telegram notification (optional)
if [ -n "$TELEGRAM_BOT_TOKEN" ] && [ -n "$TELEGRAM_CHAT_ID" ]; then
  MESSAGE="MSSQL Backup Report\n- Successful: $SUCCESS_DBS/$TOTAL_DBS databases\n- Time: $(date '+%Y-%m-%d %H:%M:%S')\n- Path: $BACKUP_PATH"
  curl -s -X POST "https://api.telegram.org/bot$TELEGRAM_BOT_TOKEN/sendMessage" \
    -d chat_id="$TELEGRAM_CHAT_ID" \
    -d text="$MESSAGE" > /dev/null
  if [ $? -eq 0 ]; then
    log_message "Telegram notification sent."
  else
    log_message "ERROR: Failed to send Telegram notification."
  fi
fi

log_message "Backup process completed."