X11 screencast (with audio)
Screenrecording of a 1024x768 pixel area, with an x/y-offset of 80/120px. Sound is recorded at a bitrate of 128kb/s from the analog input of the default ALSA sound card, the outline of the captured region is displayed on screen:
avconv -f x11grab -show_region 1 \
-s 1024x768 -i :0.0+80,120 \
-f alsa -i hw:0 \
-b:v 1200k -b:a 128k \
-y ~/screencast.mpg
Don't forget to check the mixer settings!
Recording sound from another application instead of an external source requires to modprobe the snd_aloop kernel module and a line of ALSA configuration:
### File: ~/.asoundrc
pcm.!default { type plug slave.pcm "hw:Loopback,0,0" }
Additionally, the avconv audio input parameters need to be changed to
-f alsa -i hw:Loopback,1,0
The configuration of an optional output channel for audio monitoring is described here at ffmpeg.org.
ALSA: changing audio device priority
ALSA enumerates available audio devices in the order their corresponding kernel modules are loaded, so e.g. connecting an audio capable HDMI device can break on-board sound. For a permanent and system wide change of audio device priority, this order can be manipulated by adding a simple configuration file with the suffix .conf to the folder /etc/modprobe.d/.
First it needs to get a list of the loaded sound modules:
$ cat /proc/asound/modules
0 MODULE_X
1 MODULE_Y
2 MODULE_Z
In the best case, all audio devices use different kernel modules, which will be listed, one per line, with the key options and an index value:
### File: /etc/modprobe.d/alsa.conf
options MODULE_1 index=0
options MODULE_2 index=1
options MODULE_3 index=2
If there are several audio devices based on the same chipset, additionally their associated card IDs need to be specified. The command
$ aplay -l | grep ^card
will return the necessary identifiers in the second column, right after card #:. Add them to the respective lines in /etc/modprobe.d/alsa.conf as new column three, between module name and index number.
To be prepared for the occasional use of a USB audio adapter, I suggest to additionally list the snd-usb-audio module and assign it index=0.
Here my current configuration:
### File: /etc/modprobe.d/alsa.conf
options snd-usb-audio index=0
options snd-hda-intel id=VT82xx index=1
options snd-hda-intel id=HDMI index=2
Although this is Linux, the easiest way to make the changes take effect is to reboot the system ;)
If you have several devices with the same ID, you can make ALSA directly address the hardware by adding the following entries to /etc/asound.conf or ~/asoundrc - the respective card number can again be determined with the command aplay -l.
### File: /etc/asound.conf
### OR
### ~/.asoundrc
pcm.!default {
type hw
card 1
}
ctl.!default {
type hw
card 1
}
Note: This way no other applications can access the sound card concurrently.
As a last solution, it is possible to fully disable specific cards with a line like the following in /etc/modprobe.d/alsa.conf:
### File: /etc/modprobe.d/alsa.conf
options snd-hda-intel enable=0,1
The array will disable (0) the first and enable (1) the second of two cards.
Auto-upgrade for Debian based systems
A reliable auto-updater for home use. It can be executed e.g. at boot from /etc/rc.local to keep apt based systems up-to-date. Some output will be logged to /var/log/safe-upgrade.log, in case of upgraded or held packages as well as errors a report will be sent to root@localhost.
Update August, 2020: Command line option "--full" for Dist-Upgrade.
Update June, 2022: sleep-loop for delayed connections (dial-up, WiFi).
#!/bin/sh
#
# safe-upgrade.sh
#
# automated "safe-upgrade" for apt-based distributions with logging
# to /var/log/safe-upgrade.log and a mail to root@localhost in case
# of upgraded packages or problems
# optional command line parameter "--full" will run a dist-upgrade
pingtest=debian.org
hostname=`hostname`
logfile=/var/log/safe-upgrade.log
mailto=root@localhost
if [ X"$@" = X"--full" ] ; then
task=dist-upgrade
else
task=upgrade
fi
sleep 15
echo ----- `date` ----- >> "$logfile"
ping -c 1 "$pingtest" > /dev/null 2>> "$logfile" ||\
{
echo "System upgrade cancelled: No internet connection." |\
tee -a "$logfile" |\
mailx -s "$hostname"\ update\ \*\*\*ERROR\*\*\* "$mailto"
exit 0
}
DEBIAN_FRONTEND=noninteractive
apt-get -q=2 update 2>&1 |\
tee -a "$logfile" |\
mailx -E -s "$hostname"\ update\ \*\*\*ERROR\*\*\* "$mailto"
apt-get "$task" -y -q 2>&1 |\
grep -ve "^(\{0,1\}Reading" \
-e "^Building" \
-e "^Calculating" |\
tee -a "$logfile" |\
grep -ve "^0 upgraded.*0 not upgraded\.$" |\
mailx -E -s "$hostname"\ upgrade\ log "$mailto" &&
echo ----- DONE ----- >> "$logfile"
exit 0
To tame the daily growing log file, add the following lines to /etc/logrotate.conf or into an own file in /etc/logrotate.d/. This will keep compressed archives of the last three months' log files.
### File: /etc/logrotate.conf
/var/log/safe-upgrade.log {
monthly
create
rotate 3
}
If you want the script to be executed by cron, it is necessary to set the $PATH variable - in the script itself, or in the crontab. This example runs every three hours at 45':
### File: root crontab, open to edit with "crontab -e"
# m h dom mon dow command
45 */3 * * * PATH='/usr/sbin:/usr/bin:/sbin:/bin' /path/to/safe-upgrade.sh
Piping dd
Write to several devices at once with dd and tee:
$ dd if=INFILE | tee > (dd of=/dev/sdX) | dd of=/dev/sdY
dd over the network with netcat and bzip compression (not encrypted),
serverside...
$ nc -l 9000 | bzip2 -d | dd bs=1M of=OUTFILE
...and clientside:
$ dd bs=1M if=INFILE | bzip2 -c | nc SERVER 9000
Writing data to an ssh server, using xz transport compression:
$ dd if=INFILE bs= 1M | xz |\
ssh user@host "xz -d | dd of=OUTFILE bs=1M"
Reading data from an ssh server, again with xz transport compression:
$ ssh user@host "dd if=INFILE bs=1M | xz" |\
xz -d | dd of=OUTFILE bs=1M