Answer:

If you have a very large file, sometimes you can speed up sed by using the following method:

Original method:

# sed 's/foo/bar/g' filename

Optimized method:

# sed '/foo/ s/foo/bar/g' filename

The second method is faster since substitution is only performed when the search string is found.

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Answer:

To open a file and automatically move the cursor to a particular line number

# vi +80 test.txt

The vim will move the cursor to line 80 when opened the file.

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Answer:

grep command is useful for searching file's content by a key string, e.g.

# grep foo text.txt

All the lines matching foo will be printed.

However, to only print the number of matching lines, you can use the -c flag

# grep -c foo text.txt
4

There are total 4 lines match the word foo.

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Answer:

Install Python modules cannot be easier with easy_install.

To use easy_install, you can use apt-get to install the "python-setuptools" package

# sudo apt-get install python-setuptools

Then you can use easy_install to install the module you want, e.g. pymongo

# sudo easy_install pymongo

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Answer:

The official pronunciation is "ga-nome", but most people say "nome"

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Answer:

SSHMenu is a GNOME panel applet* that keeps all your regular SSH connections within a single mouse click.

Highly recommended if you need to manage a lot of SSH sessions.

Official homepage: http://sshmenu.sourceforge.net/

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Answer:

To generate random files of fixed size (e.g. 1GB) in Linux:

dd if=/dev/zero of=test.bin bs=1000000000 count=1

You can adjust the file size by setting the bs parameter (byte size).

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Answer:

To stop other machine from pinging your machine, you the following command

# sysctl -w net.ipv4.icmp_echo_ignore_all=1

To turn it on again:

# sysctl -w net.ipv4.icmp_echo_ignore_all=0

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Answer:

Suppose a file test.txt is being locked by a program, e.g. using the flock system call, how can we know if this file is really being locked?

# lsof test.txt
COMMAND  PID USER   FD   TYPE DEVICE SIZE   NODE NAME
perl    5654 john 3uW  REG    8,1    1 983057 test.txt

The W means the file is currently held by an exclusive lock. You can find more information in the link below:

http://linux.die.net/man/2/flock

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Answer:

Assume you have a simple Python script hello.py, you want to perform syntax check. You can use the following method

# python -c 'import hello'

Traceback (most recent call last):
  File "", line 1, in 
  File "hello.py", line 1
    echo "Hello, World!"

If there is any syntax error, it will prompt out to the screen.

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