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I have a 9 year old MacBook Pro that has died. I want to recycle it, but I want to wipe any sensitive and personal data before it leaves my hands. I am only able to boot into safe (single user) mode using Cmd-S. I get the terminal prompt, but for some reason the file system is read-only. I need to change the file system to read-write so I can delete the Users files. I have exhausted my limited knowledge of commands, chown, chmod, etc. but the constant message I get is that files cannot be deleted because the file system is read-only. Is there a way to get the file system to a state where I can deleted files or even better wipe the drive completely? Thanks,

  • If the hard drive is removable on your MBP then just remove the hard drive and destroy it with a hammer, Otherwise some data can be retrieved even if overwritten. – user3439894 Jul 27 '19 at 19:12
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To make the filesystem writable, you would use mount with the u and w options.

/sbin/mount -uw / 
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The commands you want to use to change the startup drive to write where at one time print out in the boot up messages.

Deleting a file will only delete the directory information. There are tools around to recover data.

This command will create the file zero with all zeroes in it. It will run until the disk is full. Thus, writing over the data.

# to check out what disk you have available
df
# another look at the disks
diskutil list

# check where the output is going.
# use pwd print working directory
pwd

dd if=/dev/zero of=zero  bs=1024k

# dissecting this dd command
# if=/dev/zero is the input data of all zeros.
# of=zero is the name of the output file.
# bs=1024k block size of 1meg  ( 1024 * 1024 )

example run. control + c to stop

mac $ dd if=/dev/zero of=zero  bs=1024k
^C1075+0 records in
1074+0 records out
1126170624 bytes transferred in 3.054673 secs (368671422 bytes/sec)
mac RC=1 😱  $ ls -l zero
-rw-r--r--  1 mac  staff   1.0G Aug  1 15:13 zero
mac $
  • I was able to change the mount to be read/write, however when I run the dd command as specified, I get a message "dd: /: is a directory". If I substitute the "/" with "/dev/disk0s2" I get a message "Sandbox: dd(12) System Policy: deny(1) file-write-data /dev/disk0s2 //dd: disk0s2: Operation not permitted" Any suggestions are welcome.@historystamp. – wannalearn Aug 1 '19 at 16:37
  • I do not understand what is going on. I'd say you mis-typed the command. There are no spaces in "if=/dev/zero". I suspect if you had put an space in here, you would get that message. – historystamp Aug 1 '19 at 19:19

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