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Check disk for bad sectors
Checks HDD for bad sectors, just like scandisk or chkdisk under some other operating system ;-).

show installed but unused linux headers, image, or modules
will show: installed linux headers, image, or modules: /^ii/!d avoiding current kernel: /'"$(uname -r | sed "s/\(.*\)-\([^0-9]\+\)/\1/")"'/d only application names: s/^[^ ]* [^ ]* \([^ ]*\).*/\1/ avoiding stuff without a version number: /[0-9]/!d

Create a mirror of a local folder, on a remote server
Create a exact mirror of the local folder "/root/files", on remote server 'remote_server' using SSH command (listening on port 22) (all files & folders on destination server/folder will be deleted)

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"

Find the 20 biggest directories on the current filesystem
This command will tell you the 20 biggest directories starting from your working directory and skips directories on other filesystems. Useful for resolving disk space issues.

Fire CMD every time FILE (or directory) is updated (on *BSD)

Mapreduce style processing
parallel can be installed on your central node and can be used to run a command multiple times. In this example, multiple ssh connections are used to run commands. (-j is the number of jobs to run at the same time). The result can then be piped to commands to perform the "reduce" stage. (sort then uniq in this example). This example assumes "keyless ssh login" has been set up between the central node and all machines in the cluster. bashreduce may also do what you want.

Update program providing a functionality on Debian
On Debian systems, choose which command provides java. Works for all alternatives listed in /etc/alternatives.

How to estimate the storage size of all files not named *.[extension] on the current directory
With this sentence we can estimate the storage size of all files not named *.jpg on the current directory. The syntax is based on Linux, for Unix compliance use: find ./* -prune ! -name '*.jpg' -ls |awk '{TOTAL+=$7} END {print int(TOTAL/(1024^2))"MB"}' We can change the jpg extension for whatever extension what we need

ping as traceroute
This command uses ping to get the routers' IP addresses to the destination host as traceroute does. If you know what I mean..


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