[Thu Dec 29 14:53:01 2011] [crit] [client xx.xx.xx.xx] (13)Permission denied: /home/admin/domains/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable

./set_permisions.sh set_user_home username

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Within these VMs the DomU OS is once again using LVM for various reasons. This does create some headaches for taking the backup.

The basic idea is:

1. Create a snapshot Logical Volume
2. Allow the Dom0 to see the Logical Volumes within the Logical Volume (phew).
3. Mount the newly discovered Logical Volumes.
4. Take backup
5. Tidy up

There are couple of assumptions that I have made. I have assumed that you have used custom names for the Volume Groups in either (or both) the Dom0 (host) or DomU (guest). Personally, I always use a kickstart file to create my DomUs, so I have the main VG set to XenVG00. All my DomU’s are all in a VG on the Dom0 called vg_xen – this is not essential though.

The second assumption is that you have some spare space in the Volume Group holding the DomU images. It does not need to be much, as we will be removing the snapshot volume when we have finished with it.

First off, we need to create our snapshot:

[root@dom0 ~]# lvcreate -L 1G -s -n lv_snapshot/dev/vg_xen/lv_xen_snaptest

Logical volume “lv_snapshot” created

This creates a snapshot volume called lv_snapshot of the a DomU which is using a Dom0 LV called lv_xen_snaptest. This is useful in itself as you could now take an image of this LV. I do exactly this for Disaster Recovery (dd if=/dev/vg_xen/lv_snapshot | bzip2 | dd of=/path/to/dr_image.bz2). In a worst case scenario, this image could be dd’ed back into a new Logical Volume, on a new system, for a new instance of Xen to run.

What we want to do though is get to the files in this snapshot. As the DomU is using LVM, this is unfortunately non-trivial. First we have to use kpartx to extract the LV data:

[root@dom0 ~]# kpartx -av /dev/vg_xen/lv_snapshot

add map lv_snapshot1 : 0 208782 linear /dev/vg_xen/lv_snapshot 63
add map lv_snapshot2 : 0 20755980 linear /dev/vg_xen/lv_snapshot 208845

You can see 2 LVs have been found. As lv_snapshot1 is smaller, we know that is the swap file and lv_snapshot2 is the / file system. We now need to get LVM to see these LVs and activate them.

[root@dom0 ~]# vgscan

Reading all physical volumes. This may take a while…
Found volume group “vg_xen” using metadata type lvm2
Found volume group “XenVG00″ using metadata type lvm2
Found volume group “VolGroup00″ using metadata type lvm2

[root@dom0 ~]# vgchange -ay XenVG00

2 logical volume(s) in volume group “XenVG00″ now active

Now the LVs are active we can mount them as if they were any other disk.

[root@dom0 ~]# mount /dev/XenVG00/LVroot /mnt/

And run any command we like

[root@dom0 ~]# rsync -avhp /mnt/ /backup/xen_test/

Obviously we now have to clean after ourselves:

[root@dom0 ~]# umount /mnt
[root@dom0 ~]# vgchange -an XenVG00

0 logical volume(s) in volume group “XenVG00″ now active

[root@dom0 ~]# kpartx -d /dev/vg_xen/lv_snapshot
[root@dom0 ~]# lvremove /dev/vg_xen/lv_snapshot

Do you really want to remove active logical volume “lv_snapshot”? [y/n]: y
Logical volume “lv_snapshot” successfully removed

The important thing here is that we have not at any point paused our VM, but we have been able to make a full backup of it.

The size of the snapshot volume is the hard bit here. I have used a 1G snapshot LV. To give an idea of how big it needs to be: by the time a DR image of my wiki has been taken, bzipped and sent over SSH to another box for storage, the snapshot usage has reached nearly 7%.

FreeBSD version 5.0/6.0 or later

Newer version of FreeBSD has special start, stop, restart script, you can use this script restart inetd:

#/etc/rc.d/inetd restart

Old method (works on all variant of UNIX/Linux/BSD oses)
Once you made changes to inetd (internet super-server)configuration file (/etc/inetd.conf) you can use kill or killall command as follows to restart inetd:

# killall -HUP inetd

OR

# kill -HUP inetd

OR

# kill -HUP `cat /var/run/inetd.pid`

This causes the inetd program to restart and examine its configuration files. This is especially useful if you have changed the configuration settings.

Caveat

This feature is experimental. It currently requires a version of vzctl patched with this patch.

It is also necessary to run one of these 2 kernels :

• 2.6.27 briullov.1 or later
• rhel5 064.4 or later

Howto

• ppp modules need to be loaded in the HN :

HN # modprobe ppp_async
HN # modprobe ppp_deflate
HN # lsmod | grep ppp
ppp_deflate 9793 2
zlib_deflate 21977 1 ppp_deflate
ppp_async 15169 1
crc_ccitt 6337 1 ppp_async
ppp_generic 30165 6 ppp_deflate,ppp_async
slhc 10561 1 ppp_generic

• set “ppp” feature for stoppped VE:

HN # vzctl set [VEnumber] --features ppp:on --save

• start VE :

HN # vzctl start [VEnumber]

• Prepare /dev/ppp within VE:

HN # vzctl set [VEnumber] --devices c:108:0:rw --save
HN # vzctl exec [VEnumber] mknod /dev/ppp c 108 0
HN # vzctl exec [VEnumber] chmod 600 /dev/ppp

• See if it works (as root):

VE# /usr/sbin/pppd

You should see gibberish in the standard output like

    ~�}#�!}!}!} }4}”}&} } } } }%}&)Q�}4}’}”}(}”p})

If there is an error message instead, something went wrong.

• From that point, you can finish your setup as in a real hardware environment.

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1) From the Plesk control panel.  Login to Plesk >> click “Domains” >> click “domainname.tld”  >> click “WebSite Settings” >> make sure PHP support is checked, but “safe_mode” is  unchecked >> click Save.

2) The second way is to turn off sqfe_mode using vhost.conf file. Create a vhost.conf file under “/var/www/vhosts/domainname.tld/conf/” directory and place the following lines:

<Directory /home/httpd/vhosts/<domain.com>/httpdocs>
php_admin_flag safe_mode off
</Directory>

Now, in order for Plesk to read these changes, execute

/usr/local/psa/admin/bin/websrvmng -a
service httpd restart

You can enable “register_globals” for a domain the same way mentioned in the 2nd step but make sure to execute the 2 commands for the changes to take effect.

The core.xxx files are created on Linux servers and holds the current state of a process working memory when a process is crashed. To view the core.xx files in Linux, execute the command:

root@host [~]# strings core.xxx

It will list different state of a process on each line.

PHP Warning:  PHP Startup: Unable to load dynamic library ‘/usr/lib64/php/modules/ffmpeg.so’ – /usr/lib64/php/modules/ffmpeg.so:
undefined symbol: _php_create_ffmpeg_frame in Unknown on line 0

You may also notice the “PIX_FMT_RGBA32″ error message while compiling ffmpeg-php

ffmpeg-php-0.5.0/ffmpeg_frame.c:495: error: ‘PIX_FMT_RGBA32′ undeclared (first use in this function)

The above error messages is the result of incorrect function declared in the ffmpeg_frame.c file under the ffmpeg-php-0.x.0 directory.

Solution:

Goto the the ffmpeg-php-0.x.0 directory and edit the ffmpeg_frame.c file

vi ffmpeg-php-0.x.0/ffmpeg_frame.c

Now replace every instance of ‘PIX_FMT_RGBA32′ with ‘PIX_FMT_RGB32′ in the file by executing

:%s/PIX_FMT_RGBA32/PIX_FMT_RGB32

OR

replace “PIX_FMT_RGBA32″ “PIX_FMT_RGB32″ — ffmpeg_frame.c

Save the file and compile ‘ffmpeg-php’ again using the following steps

cd ffmpeg-php-0.x.0
make clean
./configure
make
make install

Once done, ffmpeg should work along with PHP now.

You might have a small office where you customise one desktop just how you like it and need to roll this out to N other PC’s or simply want a backup of a server or desktop to another machine or even to an image file.

The main tool here is netcat which is extremely powerful and has a multitude of other great uses that won’t be covered here.

Target Machine:

** Boot to linux rescue mode with networking (CentOS works fine)

Initiate netcat to listen on port 30 – # nc -l -p
| dd of=/dev/sda (assuming the hard drive is sda and not hda):

# nc -l -p 30 | dd of=/dev/sda

Source Machine:

Dump the contents of the disk to the target PC – #dd if=/dev/sda | nc

# dd if=/dev/sda | nc 192.168.0.20 30

Then to check that traffic is flowing, on the source go to another terminal (ALT/F2) and dump the tcp data on the NIC (assuming it’s eth0):

tcpdump -tnli eth0 port 30

If you just want a backup image you could change the above output on the taget to:

# nc -l -p 30 | dd of=mybackup.img

That’s it. Naturally the target PC/disk cannot be smaller than the source:) I hope this saves someone a lot of time.

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When you try and rename it the following is given:

$ mv ––index.html index.html.renamed
mv: unrecognized option `––index.html’
Try `mv ––help’ for more information.

I also tried delimiting it the normal way, but it wouldn’t work either:

    mv \–\–index.html index.html.renamed

The correct way to rename it is:

    mv ./––index.html index.html.renamed

Because –– has special meaning, you can’t delimit it with a simple backslash (\), you have to put a path reference in there to delimit it. So my path working directory (pwd) was /home/user/data/ where the file was located, so I could use ./ to reference the current pwd. The other option is to put the full path in:

    mv /home/user/data/––index.html index.html.renamed

Hopefully this helps out some other Linux server administrator out there who’s mind it has slipped.