Ubuntu postfix errot - postdrop: warning: unable to look up public/pickup: No such file or directory

Author: Infong Date: 02 Nov 2011 Category: os Comments

I installed postfix and got this error:

postdrop: warning: unable to look up public/pickup: No such file or directory.

Turns out that sendmail was previously installed and that was messing things up. I had to stop sendmail and make the appropriate directory and restart postfix.


mkfifo /var/spool/postfix/public/pickup
ps aux | grep mail
sudo /etc/init.d/postfix restart

Change the partition number on Linux

Author: Infong Date: 02 Nov 2011 Category: os Comments

When we operating partition on Linux (such as delete partitions, create partition, change partition sizes), the partition number is not in accordance with the disk partition.

As my disk partition, it’s the case above. As normal, the partition ‘/dev/sda2’ should be ‘/dev/sda3’, ‘/dev/sda3’ should be ‘/dev/sda4’ and ‘/dev/sda4’ should be ‘/dev/sda2’, the extended partition needn’t change.

Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xa9943039

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63    39070079    19535008+  83  Linux
/dev/sda2       132825420   234522623    50848602   83  Linux
/dev/sda3       234522624   625141759   195309568   83  Linux
/dev/sda4        39070080   132825419    46877670    5  Extended
/dev/sda5        39070143    42973874     1951866   82  Linux swap / Solaris
/dev/sda6        42973938    44933804      979933+  83  Linux
/dev/sda7        44933868    74236364    14651248+  83  Linux
/dev/sda8        74236428    93755339     9759456   83  Linux
/dev/sda9        93755403   132825419    19535008+  83  Linux

Partition table entries are not in disk order

SO, how to fix this issue?

There are two ways at this time:

  1. Use command ‘f’ under fdisk:

    # fidsk /dev/sda
    Command (m for help):  x #(extra functionality)
    Expert command (m for help): f #(fix partition order)
    Expert command (m for help): w #(write table to disk)
  2. Rebuild partition table

    Recommended to use testdisk, is a good partition table recovery program, on how to rebuild the partition table using testdisk, please Google to get related-information.

After fix the partition order, we should modify /etc/fstab and /boot/grub/menu.lst, so the system can find the correct partition after next reboot.

Create new group/user on FreeBSD, and other

Author: Infong Date: 02 Oct 2011 Category: os Comments

Some FreeBSD command.

Add a new user:

adduser USERNAME

Add a new group:

pw groupadd GROUPNAME

Add user to group:


Show group information:

pw groupshow GROUPNAME

Delete a user:

pw userdell USERNAME || pw userdell UID || rmuser username

If you want to use ‘su -’ to root, we should add the user to group ‘wheel’.

By default, root does not allow login with SSH, if you want to allow root login, you should modify ‘/etc/ssh/sshd_config’ as follow:

PermitRootLogin yes
PasswordAuthentication yes
AllowUsers root

Mounting a hard disk image including partitions using Linux

Author: Infong Date: 29 Sep 2011 Category: os Comments

A while ago I thought it would be a good idea to make a backup of my Linux server by just dumping the complete disk to a file. In retrospect, it would have been much easier had I just dumped the individual filesystems.

When I finally got around to using this backup, long after the 10GB disk had perished I realized that to use the loopback device to mount a filesystem it actually needs a filesystem to mount. What I had was a disk image, including partition table and individual partitions. To further complicate matters the data partition was also not the first partition inside this image.

For reference, I created this image using the Unix “dd” tool:

$ sudo dd if=/dev/had of=hda.img
30544113+0 records in
30544113+0 records out
$ sudo ls -lh
-rw-r--r-- 1 root    root  9.6G 2008-01-22 14:12 hda.img

I followed the instructions on http://www.trekweb.com/~jasonb/articles/linux_loopback.html to try and mount the partitions inside the disk image, but ran into two problems.

To mount a partition inside the disk image you need to calculate the offset of where the partition starts. You can use fdisk to show this information to you, but you need to specify the number of cylinders if you are using a disk image.

You then also need to multiply the start and end numbers with the calculated sectors to get a byte offset.

I found another tool more useful for this task, called parted. If you are using Ubuntu, you can install it with “apt-get install parted”

$ sudo parted hda.img
GNU Parted 1.7.1
Using /data/rabbit/disk_image/test2
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) unit
Unit?  [compact]? B
(parted) print
Disk /data/rabbit/disk_image/test2: 10262568959B
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number  Start        End           Size         Type     File system  Flags
1      32256B       106928639B    106896384B   primary  ext3         boot
2      106928640B   1184440319B   1077511680B  primary  linux-swap
3      1184440320B  10256924159B  9072483840B  primary  ext3
(parted) quit

Now we have the offsets and we can use those to mount the filesystems using the loopback device:

$ mount -o loop,ro,offset=32256 hda.img /mnt/rabbit

That mounted the first partition, the “boot” partition, but this didn’t have the data on it that I was looking for. Lets try to mount partition number 3.

$ sudo umount /mnt/rabbit
$ sudo mount -o loop,ro,offset=1184440320 test2 /mnt/rabbit
$ sudo mount: wrong fs type, bad option, bad superblock on /dev/loop0,
missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail  or so

Oops, that doesn’t look right. According the article referred to above if you are using a util-linux below v2.12b then you cannot specify an offset higher than 32bits. I’m using util-inux 2.13 which shouldn’t have that problem, and besides, my offset is well below the 32bit limit.

The article also offers an alternative loopback implementation that supports mounting partitions within an image, but that requires patching and recompiling your kernel which I would rather not do.

Instead I decided to extra ct the filesystem from the image which would then allow me to mount it without specifying an offset. Doing this is quite straightforward with “dd”. You need to give “dd” a skip count, or, how far into the source to start copying, and a count, how much to copy.

Here you can either use the single byte offsets retrieved with parted or divide them by 512 and let “dd” use 512 byte blocks. Copying just one byte at a time takes a very long time, so I suggest using a larger block size.

Here is the command I used to extract my filesystem. Skip is 2313360 (1184440320/512) and Count is 17719695 (9072483840/4)

$ sudo dd if=hda.img of=hda3.img bs=512 skip=2313360 count=17719695
17719695+0 records in
17719695+0 records out
9072483840 bytes (9.1 GB) copied, 485.679 seconds, 18.7 MB/s

After extracting the filesystem I was able to mount it without any problems.

$ sudo mount -o loop hda3.img /mnt/rabbit/
$ sudo df -h /mnt/rabbit
Filesystem            Size  Used Avail Use% Mounted on
8.4G  6.3G  1.7G  80% /mnt/rabbit

Upgrade kernel failed on Debian Squeeze vps

Author: Infong Date: 26 Sep 2011 Category: virtualizationos Comments

I’ve got some problems when upgrading the kernel on my VPS:

warning: grub-probe can't find drive for /dev/xvda. grub-probe: error: cannot stat `/dev/xvda'. run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 1

So I have resolved this problem like this:

  1. First let’s create /dev/xvda block device:

    $ sudo mknod /dev/xvda b 202 0
  2. Edit /boot/grub/device.map file:


    (hd0) /dev/sda


    (hd0) /dev/xvda

  3. Edit /usr/sbin/update-grub file:


    find_device ()
        if ! test -e ${device_map} ; then
            echo quit | grub --batch --no-floppy --device-map=${device_map} > /dev/null
        grub-probe --device-map=${device_map} -t device $1 2> /dev/null


    find_device ()
            if ! test -e ${device_map} ; then
                    echo quit | grub --batch --no-floppy --device-map=${device_map} > /dev/null
            #grub-probe --device-map=${device_map} -t device $1 2> /dev/null
            echo /dev/xvda
  4. Run update-grub 0

  5. Assuming your root disk is /dev/xvda1, run:

    sed -i "s/xvda/xvda1/g" /boot/grub/menu.lst

    The run ”apt-get upgrade” now.

open_basedir restriction in effect: eAccelerator and open_basedir

Author: Infong Date: 25 Sep 2011 Category: spl Comments

When I was checking my server’s apache error log, I found many warning about ‘open_basedir’ like:

2011/09/25 21:27:54 [error] 3927#0: *146 FastCGI sent in stderr: "PHP Warning: require(): open_basedir restriction in effect. File() is not within the allowed path(s): (/srv/http/:/home/:/tmp/:/usr/share/pear/) in /srv/http/xxx.php on line 913″ while reading upstream, client: x.x.x.x, server: xxxxx.com, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:/var/run/php-fpm/php-fpm.sock:", host: "xxxxx.com", referrer: "http://xxxxx.com/"

I tried everything including setting setting open_basedir. It stopped working if I activated the open_basedir protection and started working if I removed it. After doing some research, I looked into the wrong direction – the problem was not php but eAccelerator. After I found that out it was easy to get to the solution, you need to compile it with the option –without-eaccelerator-use-inode, like this:

$ cd /PATH/TO/eaccelerator-$VERSION
$ make clean
$ ./configure --enable-eaccelerator=shared --without-eaccelerator-use-inode
$ make
$ sudo make install

After re-compiling and installing, make sure you clear out the existing eAccelerator files before restarting webserver:

$ sudo rm -rf /var/cache/eaccelerator/*
$ sudo /etc/rc.d/httpd restart

OK, everything became quiet again.


  1. http://eaccelerator.net/ticket/414
  2. http://eaccelerator.net/ticket/104