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Change timestamp on a file
-a for access time, -m for modification time, -c do not create any files, -t timestamp

Read all the S.M.A.R.T. data from a hard disk drive
This is to pull all the saved S.M.A.R.T. (Self-Monitoring, Analysis and Reporting Technology) information from a hard drive. This can give you an idea of the nature and extent of an issue on a failing hard drive.

ionice limits process I/O, to keep it from swamping the system (Linux)
This command is somewhat similar to 'nice', but constrains I/O usage rather than CPU usage. In particular, the '-c3' flag tells the OS to only allow the process to do I/O when nothing else is pending. This dramatically increases the responsiveness of the rest of the system if the process is doing heavy I/O. There's also a '-p' flag, to set the priority of an already-running process.

Write comments to your history.
A null operation with the name 'comment', allowing comments to be written to HISTFILE. Prepending '#' to a command will *not* write the command to the history file, although it will be available for the current session, thus '#' is not useful for keeping track of comments past the current session.

Kill any lingering ssh processes
Also ignoring "sshd" server is necessary since you should not kill ssh server processes.

Find dead symbolic links
-L tells find to follow symbolic links, so -type l will only return links it can't follow (i.e., those that are broken).

Extend a logical volume to use up all the free space in a volume group

validate the syntax of a perl-compatible regular expression
Place the regular expression you want to validate between the forward slashes in the eval block.

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

locating packages held back, such as with "aptitude hold "
locating packages held back, such as with "aptitude hold "


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