Work Stuff

I had found C code to be around 150x faster than Matlab for my implementation of the Monte Carlo code in Matlab.

User time: 3 sec for the C program
elapsed_time = 453.2500 sec for the Matlab program

This stackoverfloe discussion has some interesting points to make - use Matlab first to get correct results, then increase speed with C, beware of errors in C libraries.

These benchmarks show python to be 3x to 100x slower than C - so, translating from Matlab to python in search of speed gains may not make sense.

These benchmarks show perl having similar speeds as python for loops - so I needn't explore perl, either.

Friday, September 16, 2016

miui permissions

On the Xiaomi Mi3 phone which runs the MIUI skin for Android, the method for setting permissions for apps is slightly different from the method for stock Android phones. The method for MIUI is via the Security App on the home screen, Security -> Permissions -> Permissions -> (Choose the type of permission like Contacts etc) -> enable or disable per app.

This is for MIUI Global 7.5, running on Android 6.0.1

Sunday, July 17, 2016

Income tax e-filing with e-verification

In earlier posts, I had detailed the process for e-filing Income tax returns in India. This year, from Assessment Year 2016-17, the verification can also be done online, by logging onto Netbanking portal of a bank where my PAN number is associated with my account. So, no need to print and post the ITR-V form.

In HDFC bank's netbanking portal, the e-verification is currently available under Requests - Income Tax E-filing on the left-hand side.

Around a month after I submitted the return in June, my tax refund has been credited, too.

Sunday, July 10, 2016

checking for bad blocks on hard disk

The IBM ThinkCentre given by K for use by Ke's son had some disk issues - the hard disk was my former 160 GB laptop hard disk. Probably bad sectors and so on, so I had to do the Linux equivalent of running scandisk. Ubuntu 16.04 apparently doesn't support shutdown -Fr now for scanning on reboot - maybe due to systemd?

So, booted using USB flash drive and ran

sudo umount /dev/sda1

sudo e2fsck -c /dev/sda1

Apparently e2fsck with the -c option marks bad blocks using the badblocks program. 160 GB drive took 1 hour 30 minutes to scan - would have taken around 45 minutes if not for the 97 errors.

Output of badblocks 97/0/0 apparently means read/write/corruption errors. Since I'm doing a read-only test, only the read errors show up.

Sunday, July 03, 2016

browsing Windows shares with Master Browser down

The Studio network's master browser was set as the local server, which now has smbd service stopped. So, smb4k, konqueror etc were not displaying shares when queried with smb hostnames like smb://hostname
- ip addresses were required.

In order to query the ip addresses, google led to this post, so a listing, albeit clunky, is obtained with
nmblookup -S WORKGROUP

where WORKGROUP should be replaced with the name of the workgroup in the network. smb4k lists the workgroup names, so that can be a first step.

Edit: PB adds a better way:
nbtscan -qe 192.168.127.0/24

Thursday, June 23, 2016

converting putty key to open ssh keys

Used the method given here to convert, using
puttygen mykeyfile.ppk -o ~/.ssh/id_rsa.pub -O public-openssh

and
puttygen mykeyfile.ppk -o ~/.ssh/id_rsa -O private-openssh

After moving the keys to .ssh, we also have to chmod 600 or else ssh will not take these keys by default. We also need to name them id_rsa and id_rsa.pub for ssh to use them by default, without having to specify ssh -i keyname username@server.

fixing dual-boot time differences

With earlier versions of Linux, the method was to choose UTC = yes in /etc/default/rc5 and so on. With Ubuntu 16.04 and above which use systemd, the method is to enter

timedatectl set-local-rtc 1

Monday, June 20, 2016

behaviour of virtualdub frame processing

If we choose Process every other frame (decimate by 2) - the resulting avi would have a framerate half that of the source.

For example, a 30fps source, with this decimate by 2 results in an output at 15 fps. If that 15 fps output is re-saved using direct stream copy choosing 30 fps as output frame rate, then we get a 2x speeded up video. A two-step process.

In order to get 2x speeded up video in one step, choose to Change frame rate to 60 fps, and then Convert to 30 fps.

Tuesday, June 14, 2016

cloning laptop hard disk

My laptop hard disk started showing SMART errors with Crystal Disk Info. Got a new Seagate 1 TB SSHD for replacement. Macrium Reflect Free could not clone - the bad sectors made it abort. Clonezilla did the job in around 4 hours for the 160 GB hard disk with three partitions, using an external USB dock for the new hard disk.

But the cloned hard disk did not boot. Booted with Windows XP install DVD, went into recovery console and did fixmbr. Then XP booted, but showed only C and D drives. Since in any case I would need to copy files from E:, might as well increase the size of C: by deleting D:. Used Partition Wizard for increasing C: size, created D: and E: as fresh partitions, and left free space for Linux. RichCopy copied over the D: and E: contents, ignoring errors, in just about 90 minutes. Now most apps work as expected, except some which complain about path not found - maybe they look for My Documents in C:.

Later, installed Kubuntu 16.04 on a trial basis, using mini.iso and a network install - the process took around 90 minutes.

Tuesday, June 07, 2016

checksums on Windows

As mentioned on this page, installed and tried out WinMD5Sum and Checksums calculator. Found that one of my iso downloads had a checksum error.

Wednesday, June 01, 2016

WHM + CPanel setting up ssh access

To set up shell access via ssh to a server for which I have Web Host Manager (WHM) and CPanel access:

1. Import my existing ssh public key to the server via the CPanel of the relevant user - by clicking Manage SSH keys - for this, as this post mentions, the key should be prefaced with ssh-rsa and should not have line breaks within the key.
2. The key should be authorized - from the Manage SSH keys interface, by clicking on the Manage authorization link. Now ssh login via key exchange using that key would be possible, for that user.
3. In order to get to a root shell, that user has to be added to the wheel group, after making sure that user is in a full shell and not a jailed shell - via WHM in Home >> Account Functions >> Manage Shell Access and Home >> Security Center >> Manage Wheel Group Users respectively.

Sunday, May 08, 2016

problems with X crashes on newer Ubuntu

My Ubuntu install has had problems with random freezes after an upgrade to 12.04. Finally, when starting to do some serious simulation work, I decided to do something about it.

The first thought was that firefox was causing the crashes, since the freezes would start most often while starting firefox. But then, found the crashes happening when starting other apps as well. Suspected X, or the display driver, and wanted to use vesa instead. Many of the methods listed, like blacklisting nouveau, did not work with 16.04 - even after reboots, nouveau driver was being listed as used by lsmod.

Final solution was to create a /etc/X11/xorg.conf - which does not exist by default. As mentioned at many places, the procedure to do this was:
Switch to a console. Ctrl+Shift+F2, for example.
Kill the display manager with sudo service lightdm stop (or whichever dm is running)
Generate a new xorg.conf with sudo X -configure
Edit the xorg.conf.new created in current directory, replacing all instances of nouveau with vesa
Move it with a rename to /etc/X11 with sudo mv xorg.conf.new /etc/X11/xorg.conf
Restart X with sudo service lightdm start

Unfortunately with Vesa, the screen refreshes are very laggy, even with Lubuntu. But no crashes.

Saturday, May 07, 2016

PsPad commenting shortcut

To toggle between comment and uncomment, Ctrl+Shift+A in PsPad.

Thursday, May 05, 2016

python using a single core for numpy

A point which came up when using pynlo:

A longish reply for the question why python uses only one core for numpy -
http://stackoverflow.com/questions/15639779/why-does-multiprocessing-use-only-a-single-core-after-i-import-numpy

In short, core affinity can be reset using
os.system("taskset -p 0xff %d" % os.getpid())
after the module imports. But this would be useful only for multi-threaded programs, of course.

Wednesday, May 04, 2016

mounting a samba share with read-write permissions

Mounting a shared network drive on our internal server running Ubuntu - to make it read and write enabled, PB reports the command to be:
sudo mount –t cifs //ip-address/Share_name /local/mount/path –o username=correct_uname,uid=local_uid,gid=local_uid

Then, the local_uid user has read + write permissions.

Edit: 11 July 2016

This post about listing hostname with ip address is useful.

Also, PB adds one more tip - for mounting shares with spaces, use single quotes
sudo mount -t cifs '//192.168.1.1/SHARE WITH SPACES' tempmount -o username=guest,password='',nounix,sec=ntlmssp

Tuesday, May 03, 2016

installing and using pynlo

Looking around for supercontinuum generation literature, came across PyNLO's documentation. Tried to install and use it. Was a bit of a struggle at first, but finally it all came together.

Issues:

Anaconda3 version 4.0 installation on Windows XP failed - reported that it failed to change path variable etc, but more importantly, the exes were not running - "this is not a valid Windows executable".
On Ubuntu 14.04, tried a direct pip install. Some dependency issues. Thought upgrading to 16.04 would help - ran out of hard disk space - 13 GB. Formatted and installed Lubuntu instead. With many hiccups on the way - like while doing a manual partitioning, we must not touch the swap space - because that is where the installer stores the installation files!
With Anaconda3 and pynlo, errors like Missing parenthesis in call to print - so had to install Anaconda2 instead.
Trying installation with pip install pynlo - installation of the required pyfftw failed with the error fftw3.h: No such file or directory - it needed libfftw2-dev as mentioned in the comments at this post.
After pynlo installed also, running the example script gave errors IOError: [Errno 2] No such file or directory: .../pynlo/media/fibers/nist_fibers.txt and on copy-pasting general_fibers.txt to nist_fibers.txt, an assertion error - pynlo/interactions/FourWaveMixing/SSFM.py, line 662, in conditional_fftshift assert chksum == np.sum(abs(x)) AssertionError

Solutions:

Currently pynlo needs Python 2.7 to run, won't run on Python3. So, install Anaconda2 and not Anaconda3.
On Windows, this page says that Windows XP is supported only for Anaconda versions 2.2 and below, so downloaded 2.2 instead of the latest.
Installing libfftw2-dev on Linux with apt-get install libfftw2-dev solved the pyfftw install issues. Similarly, on Windows, the way to install it is given at https://pypi.python.org/pypi/pyFFTW#downloads - ie. download the fftw dlls and put them in the same folder as the pyfftw wheel folder before install. The pyfftw whl file was installed as pip install wheelfile.whl without any issues.
Using the latest git code solved all the pynlo issues, using
pip install git+https://github.com/pyNLO/PyNLO.git like this post.
Git for windows was installed from https://git-scm.com/download/win
On Windows XP, everything was 32 bit, and the example took 55 seconds to run. On 64-bit Lubuntu, it ran in almost the same time. Lubuntu's desktop CPU meter indicates that it was using only one core of my dual-core Athlon, ie. 50% cpu.

freeing up space on ubuntu

This post has lots of useful information in the answers. I removed libre-office and old kernels to get 1.5 GB. For the removing the old kernels, I followed
1. uname -r to know current kernel
2. sudo apt-get remove kernelname1 kernelname2 etc after doing
sudo apt-get clean
sudo apt-get autoclean
sudo apt-get autoremove
sudo apt-get install localpurge
and
rm -Rf /tmp
etc.

The listing of all packages with sizes with
dpkg-query -W --showformat='${Installed-Size} ${Package}\n' | sort -nr | less
is also a nice trick to use.

Monday, April 25, 2016

too many files bug and php error reporting

Our audio search page had a bug where if too many files were selected, the results would not be displayed. With the help of S & B, constructed a workaround. The form was submitting all fields of the large table, instead of only submitting the hidden variables which had the fileids. So, made the main form submit to a dummy destination, and made another form with the hidden variable, submitting to the actual destination. That solved the issue, which was that there were too many fields being submitted. We did not have to change max_input_vars.

While troubleshooting, we wished to see detailed error reports. The way to do that was
ini_set('display_errors',1);
error_reporting(E_ALL);
for each php page.

Wednesday, April 06, 2016

cyberoam fail-over issue

PB had a problem where the 2nd gateway was not being automatically used as failover when the main gateway failed. Apparently it was due to the way in which Cyberoam had been configured. Tech support explained it, and PB fixed it.