linux

Recursively copying between two directories including hidden files

Sometimes we need to override large structure of directories and subdirectories with newer files.

There are two ways of copying all the files in one directory including subdirectories and hidden files to another directory:

cd /orig/dir
tar cvf - . | (cd /dest/dir; tar xvf -)

which tars up the current directory to stdout then pipes it to a subshell that first cd's to the destination directory before untarring stdin.

The second way of doing this is using cp:

yes | cp -rT /orig/dir /dest/dir 2> /dev/null

Creating a patch file with diff command

To create a patch file simply run:

diff -u functions.php.orig functions.php > a.patch

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Removing the RAID metadata

If you see the “Disk contains BIOS metadata, but is not part of any recognized BIOS RAID sets. Ignoring disk sda” error message during OS installation, then you need to remove the raid metadata the “classic” way:

dmraid -r -E /dev/sda
Do you really want to erase "pdc" ondisk metadata on /dev/sda ? [y/n] :
y

How to keep a detailed audit trail of what’s being done on your Linux systems

Intrusions can take place from both authorized (insiders) and unauthorized (outsiders) users. My personal experience shows that unhappy user can damage the system, especially when they have a shell access. Some users are little smart and removes history file (such as ~/.bash_history) but you can monitor all user executed commands.It is recommended that you log user activity using process accounting. Process accounting allows you to view every command executed by a user including CPU and memory time.

Migrate files and directories between two remote servers with rsync and progress bar

To push an archive file from local to remote server with progress bar use:


rsync --rsh -av -e 'ssh -p #####' --progress --partial file.tgz root@xxx.xxx.xx.xxx:/backup

To push the content of the directory from local to remote server recursively with progress bar use:


rsync -avz -e 'ssh -p #####' --progress --partial localdirectory/ root@xxx.xxx.xx.xxx:/backup/

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Partition X does not end on cylinder boundary

While reviewing the partion layout on one of my hard drives, I noticed a number of “Partition X does not end on cylinder boundary” messages in the fdisk output:

$ fdisk /dev/sda
Command (m for help): p

Disk /dev/sda: 80.0 GB, 80000000000 bytes
255 heads, 63 sectors/track, 9726 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0xac42ac42

Device Boot Start End Blocks Id System
/dev/sda1 * 1 26 204800 83 Linux
Partition 1 does not end on cylinder boundary.

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Monit configuration to monitor Memcached instances

Monit is a free open source utility for managing and monitoring, processes, files, directories and filesystems on a UNIX system. It is pretty easy to configure and even easier to use. It comes with a simple web server to monitor statuses of the alerts you set (with basic HTTP authentication). On Monit W’k’ you can find configuration examples for different services. Just in case you need a configuration example for Memcached instances, here is what you need.

Monit mysql monitoring problem with mysqld.pid missing

Monit is a nice tool, it lets you monitor daemons like apache and mysql, and not only sends you alerts when these services fail but also it automagically restarts those services. But I have always faced problem with having monit properly detect whether mysql is running or not. The default monit config file /etc/monit/monitrc has this entry for mysql:

check process mysql with pidfile /var/run/mysqld/mysqld.pid
group database
start program = "/etc/init.d/mysql start"
stop program = "/etc/init.d/mysql stop"
if failed host 127.0.0.1 port 3306 then restart

Locking Down Your Linux Server with APF + BFD

If you allow SSH access to your server, there are some simple steps you can take to restrict access and protect yourself from brute force attacks. Two of my favorite scripts to do this are Advanced Policy Firewall coupled with Brute Force Detection, both by R-FX Networks.

3 Steps to Perform SSH Login Without Password Using ssh-keygen & ssh-copy-id

You can login to a remote Linux server without entering password in 3 simple steps using ssky-keygen and ssh-copy-id as explained in this article. ssh-keygen creates the public and private keys. ssh-copy-id copies the local-host’s public key to the remote-host’s authorized_keys file. ssh-copy-id also assigns proper permission to the remote-host’s home, ~/.ssh, and ~/.ssh/authorized_keys. This article also explains 3 minor annoyances of using ssh-copy-id and how to use ssh-copy-id along with ssh-agent.

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