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The /tmp partition is one the common places for script kiddies and crackers alike to place trojans or scripts. Because of that you should have the /tmp partition mounted noexec. First we need to check if your /tmp is secure.

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df -h |grep tmp
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If that displays nothing then go below to create a tmp partition. If you do have a tmp partition you need to see if it mounted with noexec.

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cat /etc/fstab |grep tmp
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If there is a line that includes /tmp and noexec then it is already mounted as non-executable. You will also want to check if /var/tmp is linked to /tmp.
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ls -alh /var/ |grep tmp
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If it shows something to the effect of "tmp -> /tmp/" then you are ok. If not go ahead an remove the old /var/tmp and replace it with a sym link to /tmp.
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rm -rf /var/tmp/
ln -s /tmp/ /var/
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If you do not have any /tmp partition you will need to follow the directions below to create and mount a partition.

Create a 190Mb partition
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cd /dev/; dd if=/dev/zero of=tmpMnt bs=1024 count=200000
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Format the partion
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mke2fs /dev/tmpMnt
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Make a backup of the old data
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cp -Rp /tmp /tmp_backup
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Mount the temp filesystem
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mount -o loop,noexec,nosuid,rw /dev/tmpMnt /tmp
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Set the permissions
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chmod 0777 /tmp
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Copy the old files back
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cp -Rp /tmp_backup/* /tmp/
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Once you do that go ahead and start mysql and make sure it works ok. If it does you can add this line to the bottom of the /etc/fstab to automatically have it mounted:
/dev/tmpMnt /tmp ext2 loop,noexec,nosuid,rw 0 0

While we are at it we are going to secure /dev/shm. Look for the mount line for /dev/shm and change it to the following:
none /dev/shm tmpfs noexec,nosuid 0 0

Umount and remount /dev/shm for the changes to take effect.
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umount /dev/shm
mount /dev/shm
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Next delete the old /var/tmp and create a link to /tmp
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rm -rf /var/tmp/
ln -s /tmp/ /var/
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If everything still works fine you can go ahead and delete the /tmp_backup directory.
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rm -rf /tmp_backup
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