Linux - Bag of Tricks

Introduction

This document has many useful command.

Linux Set Time Examples

You can also simplify format using following syntax:

date +%Y%m%d -s "20081128"

To set time use the following syntax:

date +%T -s "10:13:13"

Use the following syntax to set new data and time:

date --set="STRING"

For example, set new data to 2 Oct 2006 18:00:00, type the following command as root user:

date -s "2 OCT 2006 18:00:00"

date --set="2 OCT 2006 18:00:00"

Rsync Copy Examples

This is to move files from one server to another

Ending the folder WITHOUT a “/” slash means copy that folder everything in that folder

Ending the folder WITH a “/” slash means copy everything within that folder

Example for “remote to local” location

rsync -chavzP --stats -e ssh user@remote_host:/remote_folder/dir1/ /local_folder/dir1/

Example for “local to remote” location

rsync -chavzP --stats -e ssh /local_folder/dir1/ user@remote_host:/remote_folder/dir1/

Example to add a Rsync key on the remote server

ssh-keygen -t rsa

Run the following to add the key to the remote server

ssh-copy-id -i ~/.ssh/id_rsa.pub remuser@dss-us-map-017

If the command cannot be run above you can copy the key to the remote server manually into the “authorized_keys” file

cd
cd .ssh
vi authrized_keys

Change the permissions on the local server

chmod 600 ~/.ssh/*
chmod 711 ~/.ssh
chmod 711 ~

Synology Rsync

rsync -aXHmS --syno-acl /volum1/[xxx] /volume2/[xxx]

-a, --archive archive mode; equals -rlptgoD (no -H,-A,-X)
-p, --perms preserve permissions
-X, --xattrs preserve extended attributes
-o, --owner preserve owner (super-user only)
-g, --group preserve group
--syno-acl copy Synology ACL data

I use the following options myself:
rsync -avhxWog --stats --backup --suffix $OLDSUFFIX --exclude-from=$RSYEXCL --syno-pseudo-root

No idea why I list options "og" since they're implied by -a, but it works...

Regards, Arild
PS: "rsync --help" lists all available options for rsync

Find and Replace String with sed

There are several versions of sed, with some functional differences between them. macOS uses the BSD version, while most Linux distributions come with GNU sed pre-installed by default. We’ll use the GNU version.

The general form of searching and replacing text using sed takes the following form:

sed -i 's/SEARCH_REGEX/REPLACEMENT/g' INPUTFILE

Cop

-i - By default, sed writes its output to the standard output. This option tells sed to edit files in place. If an extension is supplied (ex -i.bak), a backup of the original file is created.
s - The substitute command, probably the most used command in sed.
/ / / - Delimiter character. It can be any character but usually the slash (/) character is used.
SEARCH_REGEX - Normal string or a regular expression to search for.
REPLACEMENT - The replacement string.
g - Global replacement flag. By default, sed reads the file line by line and changes only the first occurrence of the SEARCH_REGEX on a line. When the replacement flag is provided, all occurrences are replaced.
INPUTFILE - The name of the file on which you want to run the command.

Find and Replace String with sed within vi

This is to search and replace a file globally withing vi

:%s/search_string/replacement_string/g

Kill Users in Linux

This is to be used when trying to kill users using the connection, replace the ? with the number of the session.

pkill -KILL -t pts/?

Create a CERT

First, you need to generate the private key and the Certificate Signing Request (CSR). You can do this via the openssl command:

openssl req -nodes -newkey rsa:2048 -keyout privatekey.key -out mail.csr

Then, generate a signing request

openssl x509 -req -days 365 -in mail.csr -signkey privatekey.key -out secure.crt

Create a localhost cert on the server

openssl req -newkey rsa:2048 -nodes -keyout /etc/pki/tls/private/localhost.key -x509 -days 365 -out /etc/pki/tls/certs/localhost.crt