remount an SD card with different privileges

remount.sh

#!/bin/bash

# Simple script to remount an already mounted SD card
# Also sets the readahead speed to 1024 

# Kevin Coyner
# 2016-02-26 

# # Parameters to be set
# #--------------------------------------------------------------------

# Where is the SD card mounted presently?
SDMOUNT="/var/host/media/removable/Kevin"

# How do you want the card remounted? [comma separated list of valid mount options]
REMOUNTOPTIONS="rw,exec,suid"

# Set to 1 to debug, otherwise 0
DEBUG=1

# # End parameters
# #--------------------------------------------------------------------

set -e
set -o nounset

if [[ ${DEBUG} -eq 1 ]]; then
    set +e
fi

if [[ -d $SDMOUNT ]]; then
    # see if there is a device at the SDMOUNT mount point
    # if so, then get its address
    # #--------------------------------------------------------------------

    CARDMOUNT=`mount | /bin/grep "${SDMOUNT}"` 2>&1

    if [[ -z "${CARDMOUNT}" ]]; then
      # Abort: There is no card mounted at ${SDMOUNT}
      if [[ ${DEBUG} -eq 1 ]]; then
          echo "Abort: There is no card mounted at ${SDMOUNT}"
      fi
      exit 0
    else
      # There is a card mounted at ${SDMOUNT}, get its address
      SDDEVICE=`echo ${CARDMOUNT} | cut -f1 -d' '`

      # Remount the card with different options
      sudo umount ${SDDEVICE} 2>&1
      sudo mount -t ext4 -o ${REMOUNTOPTIONS} ${SDDEVICE} ${SDMOUNT} 2>&1 

      if [[ ${DEBUG} -eq 1 ]]; then
          echo "SD device is ${SDDEVICE}"
          echo "SD mount is ${SDMOUNT}"
      fi

      # set readahead on SD card
      sudo blockdev --setra 1024 ${SDDEVICE}
      READAHEAD=`sudo blockdev --getra ${SDDEVICE}`

      if [[ ${DEBUG} -eq 1 ]]; then
          echo "Readahead for ${SDDEVICE} is now: ${READAHEAD}"
      fi
    fi
else
    # there is no directory mount point at SDMOUNT; exit
    exit 0
fi