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bash redirect

Error redirect to /dev/null

• 2>&-
• 2>/dev/null
• |&
• &>/dev/null
• >/dev/null 2>&1

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git rev-list

get latest commits for given directory

git rev-list -1 --abbrev-commit HEAD -- <dir-name>/

list all objects in git repo

git rev-list --objects --all

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# delete files in history

git filter-branch --prune-empty \
  --index-filter 'git rm -rf --cached \
  --ignore-unmatch MY-BIG-DIRECTORY-OR-FILE' \
  --tag-name-filter cat -- --all

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# www-data is non-login user
sudo su -l www-data -s '/bin/bash'

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disable apt repo

sudo sed -i 's:^deb:#deb:' /etc/apt/sources.list

remove unwanted repo:

sed -i '/^#/d' sources.list
sed -i '/^deb-src/d' sources.list
sed -i '/backports/d' sources.list

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search and replace

sed -e 's:origin:github:' -i .orig .git/config

find all config

find . -name config -depth 1 -exec sed -e 's:origin:github:' -i .orig {} \;

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nmap - port scanner

1. scanning for open ports

nmap <machine-address>

2. more verbose

nmap -v <machine-address>

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The starting logical volume (vm) is 1TB. The volume group (data) has plenty of free space. This can be queried with lvdisplay.

The following command will extend the logical volume vm under volume group data by 4 TB

lvextend -L4T /dev/data/vm
resize2fs /dev/data/vm

Run vgdisplay to confirm:

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scroll up and down

Ctrl-A [

This will activate copy mode in GNU/screen. Now, you can scroll up/down and look at your data. Use the following keys:

1. Ctrl-u and Ctrl-d scroll the display up/down by the specified amount of lines while preserving the cursor position. (Default: half screen-full).
2. Ctrl-b and Ctrl-f scroll the display up/down a full screen.

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creating swap

This is how to format swap partition

mkswap /dev/data/swap

shell output:

mkswap: /dev/data/swap: warning: don't erase bootbits sectors

on whole disk. Use -f to force.