ByteChemist » System Administration

Using SCP to transfer files

CHEMiST — Thu, 13 Aug 2009 08:17:11 +0000

Using SCP is a great way to transfer files from one machine to another. SCP uses SSH and can move files to/from localhost <-> remotehost or remotehost <-> remotehost.

SCP Syntax: localhost -> remotehost

scp /path/to/source-file user@host:/path/to/destination-file

SCP Syntax: remotehost -> remotehost

scp user@src-host:/path/to/src-file user@dest-host:/path/to/dest-file

SCP Examples

scp file.txt mydomain.com:~/mydir/file.txt
 
scp local_dir/filename myname@host1:remote_dir
 
scp local_dir/* myname@host1:remote_dir
 
scp myname@host1:remote_dir/filename .
 
scp myname@host1:remote_dir/filename  myname@host2:another_dir

Use cron and ntpdate to keep your linux server’s time updated

CHEMiST — Fri, 26 Jun 2009 03:02:59 +0000

To sync your linux server’s time with the NTP Pool Time Servers, use the following command.

ntpdate pool.ntp.org

If you’d like to sync with a time server weekly, add a new file named ntpdate-sync to /etc/cron.weekly. Then set the file permissions to 755 and set owner:group to root:root. Finally, exit set the file contents to the following.

#! /bin/sh
/usr/sbin/ntpdate pool.ntp.org

To sync on a custom schedule, add a new file named ntpdate-sync to /etc/cron.d. Then set the file permissions to 644 and set owner:group to root:root. Finally set the file contents as follows.

# /etc/cron.d/ntpdate-sync: crontab fragment for ntpdate
# Run ntpdate at 2:30AM on the first of every month
30 2 1 * * root /usr/sbin/ntpdate 2>&1 | /usr/bin/tee -a /var/log/cron/ntpdate-sync.log

Update – 10/18/09
Changed custom schedule cron example from once every 15 minutes to once per month.

Using SVN copy to branch or tag within a repository

CHEMiST — Sun, 22 Mar 2009 19:45:44 +0000

To “branch” or “tag” within a repository, use svn copy. The syntax is simple.

svn copy {SRC} {DST}

The source and destination can be either a working copy path or full URL in any combination. So to tag a revision from trunk the following command could be used.

svn copy --username myusername --password mypassword http://domain.com/svn/trunk http://domain.com/svn/tag/0.1.1332 -m "commit message"

Recover the MySQL Root Password in Linux

CHEMiST — Mon, 30 Jun 2008 23:06:05 +0000

Step 1 – At the linux shell, stop the current mysqld process, start the mysqld_safe process with –skip-grant-tables switch and login as root (no password).

/etc/init.d/mysql stop
mysqld_safe --skip-grant-tables &
mysql -u root

Step 2 – At the mysql shell set the root password and flush privileges.

USE mysql;
UPDATE user SET password=PASSWORD("new-password-here") WHERE User='root';
FLUSH PRIVILEGES;
QUIT;

Step 3 – Back at the linux shell stop the mysqld_safe process and start the normal mysqld process. At this point you should be able to successfully login as root using the password from Step 2.

/etc/init.d/mysql stop
/etc/init.d/mysql start
mysql -u root -p

Set MySQL Root Password

CHEMiST — Mon, 30 Jun 2008 22:45:11 +0000

To reset the MySQL root password, login to the mysql shell and run the following commands.

SET PASSWORD FOR root@localhost=PASSWORD('RootPasswordHere');
FLUSH PRIVILEGES;

Grant MySQL Privileges

CHEMiST — Mon, 30 Jun 2008 22:41:32 +0000

To grant all privileges to a user from any location login to the mysql shell and run the following queries.

GRANT ALL PRIVILEGES ON *.* TO username@localhost IDENTIFIED BY 'PasswordHere' WITH GRANT OPTION;
GRANT ALL PRIVILEGES ON *.* TO username@"%" IDENTIFIED BY 'PasswordHere' WITH GRANT OPTION;
FLUSH PRIVILEGES;

Apache Cache Control using mod_expires with Expires By Type

CHEMiST — Fri, 27 Jun 2008 17:14:54 +0000

Use Apache’s mod_expires to explicitly set the expiration of a file by it’s type. This will enable to browser to cache these static assets and greatly increase performance.

<IfModule mod_expires.c>
    ExpiresActive on
    ExpiresDefault "now"
    ExpiresByType text/html "now"
    ExpiresByType text/xml "now"
    ExpiresByType text/css "access plus 8 hours"
    ExpiresByType text/plain "access plus 8 hours"
    ExpiresByType application/x-javascript "access plus 8 hours"
    ExpiresByType application/x-shockwave-flash "access plus 8 hours"
    ExpiresByType application/pdf "access plus 8 hours"
    ExpiresByType image/gif "access plus 8 hours"
    ExpiresByType image/png "access plus 8 hours"
    ExpiresByType image/jpeg "access plus 8 hours"
    ExpiresByType image/x-icon "access plus 8 hours"
    ExpiresByType video/x-flv "access plus 8 hours"
    ExpiresByType video/quicktime "access plus 8 hours"
IfModule>

Using Rsync over SSH

CHEMiST — Fri, 11 Jan 2008 04:42:02 +0000

Prerequisites

First make sure that you are able to login to the remote host using ssh key authentication.

Basic Syntax

To sync files from a local directory to a remote directory use the following syntax:

rsync {options} -e ssh {source} {dest}

Example

Here is an example that exclude all .psd and .fla files:

rsync --exclude *.psd \
        --exclude *.fla \
        -avz -e ssh /local/dir/ user@remotehost:/remote/dir/

Using tar and gzip to Compress Files and Directories

CHEMiST — Wed, 09 Jan 2008 22:04:00 +0000

Create and Compress and Archive

Archive a group of files:

tar -czvf archive.tar.gz file1 file2 file3

Archive an entire directory:

tar -czvf archive.tar.gz directory/

Extract a Compressed Archive

tar -xzvf archive.tar.gz

List the Contents of a Compressed Archive

tar -tzvf archive.tar.gz

Common tar Switches

-c create a new archive
-x extract files from an archive
-t list the contents of an archive
-z filter the archive through gzip
-v verbosely list files processed
-f filename of the archive (filename must always immediately follow)

SSH Login Using Public Key Authentication

CHEMiST — Wed, 09 Jan 2008 05:36:38 +0000

Step 1: Generate Keypair on Localmachine

ssh-keygen -t dsa

When prompted for a passphrase you can leave it empty to enable logging in without a password (please note that there are potential security issues with doing this).

After confirming your passphrase at the second prompt you’ll find two new files (the keypair) in your ~/.ssh directory. The first file id_dsa is your private key, the second file id_dsa.pub your public key.

Step 2: Set Local ~/.ssh Permissions

chmod 700 ~/.ssh

Step 3: Copy Public Key to Remote Server

scp ~/.ssh/id_dsa.pub username@remoteserver:~/id_dsa.pub

Step 4: Login to Remote Server:

ssh username@remoteserver

Step 5: Update Authorized Keys on Remote Server

cat id_dsa.pub >> ~/.ssh/authorized_keys

Step 6: Set Remote ~/.ssh Permissions

chmod 600 ~/.ssh/authorized_keys

Done!

At this point you should be able to login to the remote server without using a password.

ssh username@remoteserver
 - or - 
ssh -i ~/.ssh/id_dsa username@remoteserver