Category: linux

Saving streaming audio on Linux

MONITOR=$(pactl list | egrep -A2 ‘^(\*\*\* )?Source #’ | grep ‘Name: .*\.monitor$’ | awk ‘{print $NF}’ | tail -n1)

goes to alsa_output.pci-0000_00_1b.0.analog-stereo.monitor on my system

LAMEOPTIONS=’ -s 44.1 –preset cbr 192′

Record currently playing audio:

Split into separate 1 hr files with a 3 sec overlap:
ffmpeg -ss 00:00:00 -t 01:00:03 -i foo.mp3 $1.01.mp3 -acodec copy
ffmpeg -ss 01:00:00 -t 01:00:03 -i foo.mp3 $1.02.mp3 -acodec copy

Commands from here

Spelunking partition tables with testdisk

I have my home directories on a separate drive from the OS, and after upgrading Fedora I went to remount my home directory and ran into problems. First off, the new Fedora had renamed hda as sda and so all the drive naming was off. I had my home directory disk mirrored in RAID 1, but some months ago one the the drives went bad and I dropped it from the array but left it plugged in until I had time to deal with it.

So I looked around for my home directory disk and mounted the one that had gone bad. It was working fine when I mounted it, so I didn’t notice until a few days later when it I noticed recently created files were missing and eventually figured it out.

So I could find the ‘good’ home directory disk and mount it, right? Not so easy, it turned out to have a small ext2 partition and a large LVM partition. Which is not the way it should be, it should have one partition. I mount the small one, and it throws ‘read past end of disk’ errors. It takes quite a while to figure out how to mount and read the LVM partitions. LVM is a really, really idea. The LVM tools couldn’t find a filesystem on the LVM partition, and after much hair pulling I realized that there really *wasn’t* one, that the partition shouldn’t exist. Because it was LVM, this took about 10X longer than it should have.

Now running with the hypothesis that the home directory disk had picked up a disk error in the partition table (Argg^&@$#@!), I made a backup image of the drive using dd:

dd if=/dev/hdc of=/data/hdc_copy.bin

Then I mounted the image as a loopback device:

losetup /dev/loop0 /data/hdc_copy.bin

And started working with the image to repair it. Looking around, testdisk seemed promising, so I installed it, ran it. Testdisk finds potential partitions on the disk, and lets you view the files in them to see if it has guessed right. After a few tries I found a testdisk partition that contained my home directories. At this point I used testdisk’s copy function to save the most critical recently (no backup) changed directories. This worked and I was hopeful. Then I had testdisk write the partition it had found to the disk image.

Now running fdisk on /dev/loop0 shows the single partition (/dev/loop0p1) spanning the whole disk as expected. /dev/loop0 can’t be mounted by itself as it is an image of the disk, not a file system (/dev/loop0p1 isn’t a device in /dev, just a fdisk label). So I had to mount the partition as a second loopback device using the info from fdisk to find the correct offset:

Disk /dev/loop0: 203.9 GB, 203928109056 bytes
1 heads, 1 sectors/track, 398297088 cylinders, total 398297088 sectors
Units = cylinders of 1 * 512 = 512 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
/dev/loop0p1 64 398283327 199141632 83 Linux

So I tried an offset of 64 * 512 = 32768:

losetup -o 32768 /dev/loop1 /dev/loop0

and then ran e2fsck on /dev/loop0. But e2fsck wasn’t happy, and none of the alternate superblocks worked either. Finally I found a reference to doing this that mentioned setting fdisk to sectors first:

Command (m for help): u
Changing display/entry units to sectors

Command (m for help): p

Disk /dev/loop0: 203.9 GB, 203928109056 bytes
1 heads, 1 sectors/track, 398297088 cylinders, total 398297088 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
/dev/loop0p1 63 398283326 199141632 83 Linux

Ah ha, the sector offset is *really* 63, so 63 * 512 = 32256 bytes, and after

losetup -o 32256 /dev/loop1 /dev/loop0

e2fsck now sees the file system and works! BTW sending e2fsck the SIGUSR1 signal makes it show a progress bar:

kill -s SIGUSR1 <e2fsck pid>

and after e2fsck completes I can mount the now good file system:

mount /dev/loop1 /mnt/home_recover
and it works!

With a good copy of the home directory filesystem I now was willing to risk changing the original drive, and ran testdisk and e2fsck on it following the same course. I was able to fix the partition table, clean the filesystem, and mount it! My home directories are all back!

Scanning and posting photos

I scanned in a bunch of family photos, fixed them up, added captions, and posted them on Google’s Picasa Web Album.

I used a flatbed scanner and filled it with photos each scan. This necessitated splitting and cropping each scan into separate images. To speed this along I wrote an AppleScript to call Photoshop’s “Crop and Straighten Photos” function and then save the images.

split_img Applescript

The script worked pretty well for about half the images. I went through and cropped/straightened each image. Then I automatically ran Auto Levels and Auto Contrast or Auto Colors on each image using a second Applescript.

adjust_img Applescript

I wanted to add captions and tags to each image using a list of captions I made when I scanned the photos. Jpg images can store this meta data in the file using the IPTC standard. Unfortunately, Google’s Picasa uploading applications terribly buggy and don’t work well with IPTC tags added by other programs like iPhoto or EXIFutils. So I couldn’t use Google’s Picasa software or plugins to upload the photos.

Google makes an API for interacting with their web sites available, and there is a Perl module, Net::Google::PicasaWeb, available that allows adding captions and tags when uploading pictures. Testing showed that it worked so I wrote a small Perl program to take a tab-delimited text file of images, the target album, the caption, and any tags and load the photos onto the Picasa Web Album site. I needed to use the most up to date version of Net::Google::PicasaWeb and make a one line change.

picasa_upload Perl program

My Picasa Web Album:

Old family photos (Jan. 2009)

RAID1 recovery

One of the MA database systems went down. It wouldn’t boot, so we put in the install disk, ‘linux rescue’ at the prompt, and it booted into rescue mode. The system is set up with the system files on a pair of RAID1 SATA drives. Drive /dev/sda was gone–fdisk found no partition. /dev/sdb was fine. I looked around for hacking traces but found nothing. /var/log/messages indicated the system had shutdown for reboot two days before. We hadn’t done it, so how/why?

First, I re-partitioned /dev/sda to look like /dev/sdb using the same ‘fd’ RAID partition type.

To bring it back up, I shut down, switched the sda and sdb cables so we could boot off the good drive and then have RAID restore the second drive. The original /dev/sdb didn’t have grub installed on the MBR, so I had to reboot with the rescue disk and reinstall grub.

grub>root (hd0,0)
grub>setup (hd0)

I had to use grub because grub-install wasn’t available from the rescue environment and /mnt/sysimage/sbin/grub-install couldn’t find /sbin/grub.

Then reboot, grub comes up, the system boots. The root /dev/md1 RAID1 is degraded as this shows, so add /dev/sdb back:

mdadm --query --detail /dev/md1

mdadm --add /dev/md1 /dev/sdb

And 20 minutes later the array is clean!

vnc to linux vncserver

Figured out how to VNC from my laptop to my linux server. Forwarded X conections were too slow so I gave VNC a try. It was harder to set up than I expected. I googled around and after many tries found a post online that worked.

Here’s the stiuation. I need to connect to my lab computer from my laptop at home. The lab computer is behind UK’s firewall. Run vncserver on the lab computer–that’s the easy part. It runs on display :1 by default:> vncserver

Turns out I need to enable port forwarding on the lab computer’s sshd:
As root add this line to /etc/ssh/sshd_config

AllowTcpForwarding yes

then restart sshd:
/etc/rc.d/init.d/sshd restart

Then forward the ssh connection. On my laptop I run this command from a terminal:

ssh -L 5901:localhost:5901

And run the VNC client. My laptop runs OS X, so I downloaded “Chicken of the VNC. By default it uses port 5900, enter display 1 (so it goes to 5900+1 = 5901) and the host is localhost. Starts up and runs fast!

Install new hard drives with Software RAID 1

This turned out to be pretty straightforward once I got the order of steps right. Don’t make the filesystems before the mkraid, you will end up with “bad superblock” errors later.

I added two 400Gb SATA hard drives in RAID1 to an existing system. I already had one pair of drives in RAID 1, the new drives form a new RAID array.

1) Phyiscally add the drives.

2) Run fdisk, make one partition on each drive.
fdisk /dev/hdc
fdisk /dev/hdd

3) Edit /etc/raidtab, add section for /dev/md1:
raiddev /dev/md1
raid-level 1
nr-raid-disks 2
chunk-size 256
persistent-superblock 1
nr-spare-disks 0
device /dev/sdc1
raid-disk 0
device /dev/sdd1
raid-disk 1

4) Make RAID, needed ‘force’ flag:
mkraid -f /dev/md1
mkraid -R /dev/md1

5) Make filesystems:
mke2fs -j /dev/sdc1
mke2fs -j /dev/sdd1

This takes 10 min or so.

6) Add new filesystem to /etc/fstab for automounting:
/dev/md1 /home ext3 defaults 1 2

And now the keychain drive gets pushed from sdc to sde:
/udev/sde1 /mnt/key vfat owner,kudzu 0 0

7) Mount new RAID:
mkdir /data
mount /data

Useful RAID commands:
more /proc/mdstat
mdadm -D /dev/md1

Useful guide:

Kernel upgrade

Upgraded the kernel on my linux server and it was the easiest thing ever:

yum upgrade kernel-smp

It updated grub and everything! Color me surprised. Linux is getting *so* easy to use.