Skype

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Installing and Running Skype

Install skype from the official repositories. If you have a 64-bit system, enable the multilib repository first as Skype is 32-bit only. For OSS-users, skype-oss is available.

Running Skype is just as easy. Type skype into a terminal or double-click the Skype icon on your desktop or in your DE's application menu.

Securing Skype

There are a couple of reasons you might want to restrict Skype's access to your computer:

  • The skype binary is disguised against decompiling, so nobody is (still) able to reproduce what it really does.
  • It produces encrypted traffic even when you are not actively using Skype.
  • ...

See [1] for more information.

AppArmor

Follow the instructions here to set up AppArmor.

The userland tools for AppArmor come with a collection of example profiles. Skype is amongst them. Copy this to the directory where AppArmor profiles are stored.

# cp -ip /etc/apparmor/profiles/extras/usr.bin.skype /etc/apparmor.d/

For whatever reason, the profile is not complete. You may wish to modify it further. Here is an example, and here is another one for Skype4. (If the Mozilla denials annoy you, feel free to uncomment the appropriate lines.)

To use the profile, first be sure securityfs is mounted,

# mount -t securityfs securityfs /sys/kernel/security

Load the profile by the command,

# apparmor_parser -r /etc/apparmor.d/usr.bin.skype

Now you can run Skype restricted but as your own user. Denials are logged in messages.log.

TOMOYO

Follow the instructions here to install TOMOYO. Please note that this section describes using TOMOYO 2.5.

During Skype audit it was discovered that Skype reads DMI information and Mozilla profile. To give Skype minimal access to your system using TOMOYO, please follow these steps.

  • Open /etc/tomoyo/exception_policy.conf file and add these lines:
path_group SKYPE_DIRS /home/\*/.Skype/
path_group SKYPE_DIRS /home/\*/.Skype/\{\*\}/
path_group SKYPE_DIRS /home/\*/.config/Skype/\{\*\}/
path_group SKYPE_DIRS /usr/share/skype/\{\*\}/
path_group SKYPE_DIRS /home/pf/work/tmp/\{\*\}/
path_group SKYPE_FILES /home/\*/.Skype/\{\*\}/\*
path_group SKYPE_FILES /home/\*/.config/Skype/\{\*\}/\*
path_group SKYPE_FILES /usr/share/skype/\{\*\}/\*
path_group SKYPE_FILES /home/pf/work/tmp/\{\*\}/\*
path_group SKYPE_FILES /home/\*/.Skype/\*
path_group SKYPE_FILES /home/\*/.config/Skype/\*
path_group SKYPE_FILES /usr/share/skype/\*
path_group SKYPE_FILES /home/pf/work/tmp/\*
path_group ICONS_DIRS /usr/share/icons/\{\*\}/
path_group ICONS_FILES /usr/share/icons/\{\*\}/\*
path_group ICONS_FILES /usr/share/icons/\*
initialize_domain /usr/bin/skype from any
initialize_domain /usr/lib32/skype/skype from any

Note that /home/pf/work/tmp folder is only the folder to which Skype will be able to save received files and from which it will be able to send all files. You have to change this folder.

  • Then open /etc/tomoyo/domain_policy.conf and add the following lines:
<kernel> /usr/bin/skype
use_profile 3
use_group 0

misc env \*
file read /bin/bash
file read /usr/bin/bash
file read/write /dev/tty
file read /usr/lib/locale/locale-archive
file read /usr/lib/gconv/gconv-modules
file read /usr/bin/skype
file read /usr/lib32/skype/skype
file execute /usr/lib32/skype/skype exec.realpath="/usr/lib32/skype/skype" exec.argv[0]="/usr/lib32/skype/skype"

<kernel> /usr/lib32/skype/skype
use_profile 3
use_group 0

file append /dev/snd/pcm\*
file chmod /home/\*/.Skype/ 0700
file create /home/\*/.cache/fontconfig/\* 0600-0666
file create /tmp/qtsingleapp-\*-lockfile 0600-0666
file create @SKYPE_FILES 0600-0666
file execute /usr/bin/firefox
file execute /usr/bin/gnome-open
file execute /usr/bin/notify-send
file execute /usr/bin/opera
file execute /usr/bin/xdg-open
file ioctl /dev/snd/\* 0-0xFFFFFFFFFFFFFFFF
file ioctl /dev/video0 0-0xFFFFFFFFFFFFFFFF
file ioctl anon_inode:inotify 0x541B
file ioctl socket:[family=1:type=2:protocol=0] 0x8910
file ioctl socket:[family=1:type=2:protocol=0] 0x8933
file ioctl socket:[family=2:type=1:protocol=6] 0x541B
file ioctl socket:[family=2:type=2:protocol=17] 0x541B
file ioctl socket:[family=2:type=2:protocol=17] 0x8912
file ioctl socket:[family=2:type=2:protocol=17] 0x8927
file ioctl socket:[family=2:type=2:protocol=17] 0x8B01
file link /home/\*/.cache/fontconfig/\* /home/\*/.cache/fontconfig/\*
file mkdir /home/\*/.cache/fontconfig/\* 0600
file mkdir @SKYPE_DIRS 0700-0777
file mksock /tmp/qtsingleapp-\* 0755
file read /dev/urandom
file read /etc/fonts/conf.avail/\*.conf
file read /etc/fonts/conf.d/\*.conf
file read /etc/fonts/fonts.conf
file read /etc/group
file read /etc/host.conf
file read /etc/hosts
file read /etc/machine-id
file read /etc/nsswitch.conf
file read /etc/passwd
file read /etc/resolv.conf
file read /home/\*/.ICEauthority
file read /home/\*/.XCompose
file read /home/\*/.Xauthority
file read /home/\*/.Xdefaults
file read /home/\*/.fontconfig/\*
file read /home/\*/.config/fontconfig/\*
file read /usr/lib/locale/locale-archive
file read /usr/lib32/gconv/UTF-16.so
file read /usr/lib32/gconv/gconv-modules
file read /usr/lib32/libv4l/v4l2convert.so
file read /usr/lib32/qt/plugins/bearer/libq\*bearer.so
file read /usr/lib32/qt/plugins/iconengines/libqsvgicon.so
file read /usr/lib32/qt/plugins/imageformats/libq\*.so
file read /usr/lib32/qt/plugins/inputmethods/libqimsw-multi.so
file read /usr/lib32/skype/skype
file read /usr/share/X11/locale/\*/Compose
file read /usr/share/X11/locale/\*/XLC_LOCALE
file read /usr/share/X11/locale/compose.dir
file read /usr/share/X11/locale/locale.alias
file read /usr/share/X11/locale/locale.dir
file read /usr/share/alsa/alsa.conf
file read /usr/share/alsa/cards/\*.conf
file read /usr/share/alsa/pcm/\*.conf
file read /usr/share/fonts/\*/\*/\*
file read @ICONS_FILES
file read proc:/cpuinfo
file read proc:/stat
file read proc:/sys/kernel/osrelease
file read proc:/sys/kernel/ostype
file read sysfs:/devices/\*/\*/\*/\*/\*/\*/modalias
file read sysfs:/devices/\*/\*/\*/\*/\*/\*/video4linux/video0/dev
file read sysfs:/devices/\*/\*/\*/\*/\*/idProduct
file read sysfs:/devices/\*/\*/\*/\*/\*/idVendor
file read sysfs:/devices/\*/\*/\*/\*/\*/speed
file read sysfs:/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
file read sysfs:/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
file read sysfs:/devices/system/cpu/online
file read/write /dev/snd/\*
file read/write /dev/video0
file read/write/truncate /home/\*/.config/Trolltech.conf
file read/write/unlink /home/\*/.cache/fontconfig/\*
file read/write/unlink /tmp/qtsingleapp-\*
file read/write/unlink/truncate @SKYPE_FILES
file rename /home/\*/.cache/fontconfig/\* /home/\*/.cache/fontconfig/\*
file rename @SKYPE_DIRS @SKYPE_DIRS
file rename @SKYPE_FILES @SKYPE_FILES
file rmdir @SKYPE_DIRS
misc env \*
network inet dgram bind 0.0.0.0 0-65535
network inet dgram bind 127.0.0.1 0
network inet dgram bind/send 0.0.0.0-255.255.255.255 0-65535
network inet stream bind/listen 0.0.0.0 0-65535
network inet stream connect 0.0.0.0-255.255.255.255 0-65535
network unix stream bind/listen /tmp/qtsingleapp-\*
network unix stream connect /tmp/.ICE-unix/\*
network unix stream connect /tmp/qtsingleapp-\*
network unix stream connect /var/run/dbus/system_bus_socket
network unix stream connect /var/run/nscd/socket
network unix stream connect \000/tmp/.ICE-unix/\*
network unix stream connect \000/tmp/.X11-unix/X0
network unix stream connect \000/tmp/dbus-\*

<kernel> /usr/lib32/skype/skype /usr/bin/xdg-open
use_profile 0
use_group 0


<kernel> /usr/lib32/skype/skype /usr/bin/gnome-open
use_profile 0
use_group 0

<kernel> /usr/lib32/skype/skype /usr/bin/notify-send
use_profile 0
use_group 0
  • After finishing editing reload TOMOYO config files by executing these commands:
# tomoyo-loadpolicy -df </etc/tomoyo/domain_policy.conf
# tomoyo-loadpolicy -ef </etc/tomoyo/exception_policy.conf

Voilà — your Skype is sandboxed now.

Please note that this config is generated on 64-bit Arch system, and some of your ioctls and library paths may differ from mentioned above. So in order to fine-tune TOMOYO config for your Skype load tomoyo-auditd daemon:

# systemctl start tomoyo-auditd

Then go to /var/log/tomoyo folder and start watching reject_003.log:

tail -f reject_003.log

The output of this command will show you rejected actions for Skype, so you'll be able to add them to domain_policy.conf file if needed.

Detailed guide about TOMOYO configuring can be found here.

Use Skype with special user

Instead of using AppArmor or TOMOYO which require the installation of extra packages, one may prefer to add a special user. This user is only used for running Skype within one's normal environment. This approach restricts Skype to reading only the data of this particular user instead of one's main user. (The new user should not be used for any other thing. Skype only.)

An AUR package, skype-restricted exists that will run skype as a separate user ("_skype") cleanly. It's heavily based on the information in this section.

Optionally, we first add a default group for the skype user. I will call the new user and its default group "skype". The security advantage in keeping the "skype" user in its separate group is that it can be restricted from accessing some places other users are allowed in.

# groupadd skype

Then we have to add the new user:

# useradd

Enter the details for the new user (assumed login name: "skype"). If you created the default "skype" group and want to keep "skype" outside the "users" group, enter "skype" when the wizard asks for the initial group. As additional groups we need "audio,video,pulse-access,pulse-rt".

Now add the following line to /home/skype/.bashrc:

export DISPLAY=":0.0"

At last we define the alias (e.g. in ~/.bashrc):

alias skype='xhost +local: && su skype -c skype'

Now we can start Skype as the newly created user simply by running skype from the command line and entering the password of the user skype.

If you are tired of typing in the skype user's password every time, make sure you installed the sudo package, run visudo then add this line at the bottom:

%wheel ALL=(skype) NOPASSWD: /usr/bin/skype

And use this alias to launch skype:

alias skype='xhost +local: && sudo -u skype /usr/bin/skype'
Note: If you forget the xhost command, Skype may fail with a "No protocol specified" error on stdout.

I noticed that the newly created user is able to read some of the files in my home directory because the permissions were a+r, so I changed them manually to a-r u+r and changed umask from 022 to 066.

In order to restrict user "skype" accessing your external drive mounted in /media/data for instance, make sure first that "skype" does not belong to group "users" (if you used the default group "skype", everything should be fine), then change the accesses on the mount point:

# chown :users /media/data
# chmod o-rwx /media/data

This way, it is ensured that only the owner (normally "root") and "users" can access the specified directory tree while the others, including "skype", will be forbidden.

Open URLs in your user's browser

When one clicks URL in chat window, skype execute xdg-open to handle it. By default xdg-open uses default web browser for skype user environment. In order to open links in your user's browser perform next setup.

Note: sudo should be installed and properly configured
Note: Current example uses firefox as preferred browser
Note: Do not forget to adjust YOUR_USER to proper value

Log in as skype user:

$ sudo su - skype

Create local preferences dir:

$ mkdir -p ~/.local/share/applications

Create /home/skype/.local/share/applications/firefox-sudo.desktop file:

[Desktop Entry]
Name=Firefox
Exec=/home/skype/firefox-wrapper %u
Terminal=false
Type=Application
Categories=Network;WebBrowser;

Set firefox-sudo.desktop to manage HTTP and HTTPS URLs:

$ xdg-mime default firefox-sudo.desktop x-scheme-handler/http
$ xdg-mime default firefox-sudo.desktop x-scheme-handler/https

(Optionally) add FTP handler:

$ xdg-mime default firefox-sudo.desktop x-scheme-handler/ftp

Create /home/skype/firefox-wrapper script (adjust YOUR_USER):

#!/bin/bash
DISPLAY=:0.0 HOME=/home/YOUR_USER sudo -u YOUR_USER /usr/lib/firefox/firefox -new-tab $1

Make it executable:

$ chmod +x ~/firefox-wrapper

Now as root user open /etc/sudoers:

# visudo

And add permission for skype user to exec user's browser (adjust YOUR_USER):

skype ALL=(YOUR_USER) NOPASSWD: /usr/lib/firefox/firefox -new-tab http*, /usr/lib/firefox/firefox -new-tab ftp*

Access received files

By default skype stores received files with 600 permissions (only owner can access them). One may use incron to perform automatic permission fix upon downloading.

Note: This example assumes that you configure skype to save received files into /home/skype/downloads

Make skype home dir and download dir accessible:

# chmod 755 /home/skype /home/skype/downloads

Install incron, enable and start it:

# pacman -Syy incron
# systemctl enable incron
# systemctl start incron

Open incrontab for root user:

# incrontab -e

Add incron job:

/home/skype/downloads IN_CREATE chmod 644 $@/$#

Save changes and exit incrontab editor.

To test incron in action just enter skype donwload dir and create test file:

# cd /home/skype/downloads
# install -m 600 /dev/null test.txt
# ls -l test.txt

File permissions should be 644 or -rw-r--r--

(Optionally) link skype download dir into your home dir:

$ ln -s /home/skype/downloads ~/skype_files

Skype Sound

Skype supports PulseAudio since version 2.1 and ALSA since version 2.0. Earlier versions support only the deprecated OSS.

Skype PulseAudio Sound (2.1+)

Sound should work out of the box, if not you can select another input using pavucontrol (you may have to install it first).

If you are on x86_64 and use the multilib skype package, you also need lib32-libpulse.

Skype ALSA Sound (2.0+)

Sound should work out of the box, if not you can select a sound device to use in Skype options. If you have problems with Skype blocking your sound device, you only need to add the following to your ~/.asoundrc

pcm.dmixout {
  # Just pass this on to the system dmix
  type plug
  slave {
     pcm "dmix"
  }
}

then you can start Skype as normal, go to the audio options and select dmixout as your speaker- and ringingdevice.

Skype-OSS Sound (Pre-2.0)

If you have a recent version of Skype, this will not work and is not needed, look at the "important notes" on start of this page. Option B is preferred over other options. With option B you can use Skype AND let other programs play sound too. With option C you can do that too, but option B is way easier to set up.

You can install the legacy skype-oss from Comunity repo.

If you need 64x-86x support then download an OSS compatible version from here and the PKGBUILD form here. Also install lib32-libxinerama. Finally, run

$ makepkg -s

to create the pacman installable package.

A. With OSS or Kernel OSS emulation for ALSA

Start Skype and make sure no other program is using your soundcard. If you want to use Skype AND let another program play sound too, look at option B instead.

B. Making ALSA + dMix work for Skype

First of all, we need to install the alsa-oss package with pacman:

# pacman -S alsa-oss

Add the following to ~/.asoundrc. If the file does not exist yet, just create it! (Many thanks to Lorenzo Colitti for figuring this out!)

# .asoundrc to use skype at the same time as other audio apps like xmms
#
# Successfully tested on an IBM x40 with i810_audio using Linux 2.6.15 and
# Debian unstable with skype 1.2.0.18-API. No sound daemons (asound, esd, etc.)
# running. However, YMMV.
#
# For background, see:
#
# https://bugtrack.alsa-project.org/alsa-bug/view.php?id=1228
# https://bugtrack.alsa-project.org/alsa-bug/view.php?id=1224
#
# (C) 2006-06-03 Lorenzo Colitti - http://www.colitti.com/lorenzo/
# Licensed under the GPLv2 or later

pcm.skype {
   type asym
   playback.pcm "skypeout"
   capture.pcm "skypein"
}

pcm.skypein {
   # Convert from 8-bit unsigned mono (default format set by aoss when
   # /dev/dsp is opened) to 16-bit signed stereo (expected by dsnoop)
   #
   # We cannot just use a "plug" plugin because although the open will
   # succeed, the buffer sizes will be wrong and we will hear no sound at
   # all.
   type route
   slave {
      pcm "skypedsnoop"
      format S16_LE
   }
   ttable {
      0 {0 0.5}
      1 {0 0.5}
   }
}

pcm.skypeout {
   # Just pass this on to the system dmix
   type plug
   slave {
      pcm "dmix"
   }
}

pcm.skypedsnoop {
   type dsnoop
   ipc_key 1133
   slave {
      # "Magic" buffer values to get skype audio to work
      # If these are not set, opening /dev/dsp succeeds but no sound
      # will be heard. According to the ALSA developers this is due
      # to skype abusing the OSS API.
      pcm "hw:0,0"
      period_size 256
      periods 16
      buffer_size 16384
   }
   bindings {
      0 0
   }
}

If you get the error message :

The dmix plugin supports only playback stream

then add the following to .asoundrc:

pcm.asymed {
        type asym
        playback.pcm "dmix"
        capture.pcm "dsnoop"
}

pcm.!default {
        type plug
        slave.pcm "asymed"
}


Now run Skype in this way each time you want to use it:

ALSA_OSS_PCM_DEVICE="skype" aoss skype

Optionally you can make a script to start Skype:

As root, create the file: /usr/bin/askype

# Little script to run Skype correctly using the modified .asoundrc
# See: https://wiki.archlinux.org/index.php/Skype for more information!
#
# Questions/Remarks: profox@debianbox.be

ALSA_OSS_PCM_DEVICE="skype" aoss skype

Now make sure every user is able to execute the file:

# chmod a+x /usr/bin/askype

You can also fix the menu entry so you can start Skype from the your window manager's menu:

Edit the file: /usr/share/applications/skype.desktop

[Desktop Entry]
Name=Skype
Comment=P2P software for high-quality voice communication
Exec=askype
Icon=skype.png
Terminal=0
Type=Application
Encoding=UTF-8
Categories=Network;Application;

Sometimes it takes a while for Skype to start up but once it is loaded it should work ok!

C. Using OSS emulation with oss2jack

oss2jackAUR is another way to have OSS emulation without using ALSA directly. Instead, oss2jack creates a OSS device that forwards everything to JACK (JACK Audio Connection Kit), which in turn mixes, then outputs to the standard ALSA device.

Skype plugin for Pidgin

See Pidgin#Skype plugin.

Problems

Skype crashes immediately

Try creating the directory

~/.Skype/Logs

Skype crashes shortly after login

If Skype crashes shortly after logging in, changing the rights for libpulse.so.0.12.4 (minor version might differ) and libpulse-simple.so.0.0.3 might fix the issue.[2]

# cd /usr/lib
# chmod ugo-r libpulse.so.0.12.*
# chmod ugo-r libpulse-simple.so.0.0.3

64bit users might have to cd to /usr/lib32 instead.

I can receive multiple audio streams, but I can only send one

Skype can send and receive audio and I still hear other sounds playing from other applications, but I cannot record my microphone with other applications. That is because Skype or aoss blocks the audio input for itself.

No video with GSPCA webcams

For i686, install v4l-utils, userspace tools and conversion library for Video 4 Linux, and run Skype with

LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so skype

to start Skype with v4l1 compatibility.

For x86_64, install lib32-v4l-utils from [multilib] repository and run Skype with

LD_PRELOAD=/usr/lib32/libv4l/v4l1compat.so skype

To make it running from DE menus and independent of Skype updates, you can add alias (e.g. in ~/.bashrc):

alias skype='LD_PRELOAD=/usr/libxx/libv4l/v4l1compat.so skype'

where `libxx' should be edited as appropriate.

No video with Compiz

Try this

$ XLIB_SKIP_ARGB_VISUALS=1 skype

Skype does not use my GTK theme, even though other Qt apps do

Recent versions of Skype allow you to change the theme via the Options menu. However, selecting the GTK+ option may not work properly. This is probably because you do not have a 32-bit theme engine installed. Try to find the engine your theme uses in the multilib repository or the AUR. If you have no idea which engine your theme is using, the easiest fix is to install lib32-gtk-enginesAUR. This does however contain quite a lot of packages, so the best would be to find and install only the needed package.

Note: You may not have to install lib32-gtk-engines. First try if the following steps work for you if you only install lib32-gtk2 and a gtk2 theme respectively. See also the forums.

Once installed, it will still not work unless you have a 32-bit version of GConf installed. You could build and install lib32-gconfAUR if desired, but there is an easier workaround. First, create or edit ~/.gtkrc-2.0 so that it contains the following line:

$ gtk-theme-name = "My Theme"

Replace My Theme by the name of your theme, but leave the quotes. Second, run Skype like this:

$ export GTK2_RC_FILES="/etc/gtk-2.0/gtkrc:$HOME/.gtkrc-2.0"
$ skype

The GTK+ theme should now appear correctly. You can make this permanent either by running Skype from a script containing the above 2 lines, or by exporting GTK2_RC_FILES in ~/.xprofile or ~/.xinitrc, depending on how you start X.

If you cannot change the theme in the Options menu, run Skype using the following command:

$ /usr/bin/skype --disable-cleanlooks -style GTK

If you wish menus within desktop environments to load Skype with a GTK theme by default then modify the 'Exec' line of /usr/share/applications/skype.desktop so that it reads:

$ Exec=/usr/bin/skype --disable-cleanlooks -style GTK

Similarly if you have set Skype to autostart then modify ~/.config/autostart/skype.desktop in the same way.

The microphone does not work

Run amixer,

$ amixer

and check if you have an output for Capture similar to the one below.

Simple mixer control 'Capture',0
 Capabilities: cvolume cswitch penum
 Capture channels: Front Left - Front Right
 Limits: Capture 0 - 15
 Front Left: Capture 8 [53%] [12.00dB] [on]
 Front Right: Capture 8 [53%] [12.00dB] [on]

If your output is similar, your microphone is working just fine, and the issue is either hardware related (broken microphone) or your volume needs to be checked. If you do not have an output similar to the one above or, more specifically, if both Front Left and Front Right are 0% or show an [off] tag at the end, then your microphone settings need to be rectified.

In either case, try to run:

$ alsamixer

and press F5 to show all channels. Using the arrow keys navigate all the way to the end and increase Capture. If you do not see a left and right channel for Capture, press the space bar. Doing this turns the left and right channels on. Check that Input Source is set to the correct value (e.g. [Front Mic]): navigate through the values with up and down arrow keys. If your microphone is an array built into your monitor, or you have a similar setup, make sure to increase the volume for the Digital column too. If you have multiple microphones, you may have to play around with the Mic Jack channel to get your desired setting.

You may want to save your mixer settings with:

# alsactl -f /var/lib/alsa/asound.state store

No incoming video stream

If skype shows a black square for the video preview, but something else (like xawtv -c /dev/video0) shows video correctly, you might need to start skype with:

export XLIB_SKIP_ARGB_VISUALS=1 && skype

Another possible workaround is to preload v4l1compat.so

LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so skype

Low sound in Skype, but works everywhere else

If you are sure your microphone is configured correct in ALSA (try recording with a 3rd-party-utility to determent whether it is an ALSA, or Skype problem), it is most likely because Skype is controlling your volume levels. Simply disable this feature in the voice settings page in the Skype configuration window.

This may also help if your microphone input is automatically lowered until 0.

Monster/low-octave "growling" distortion over mic

Some users with newer kernels are experiencing a monster-like growling distortion of their sound stream on the other end of Skype. This can be fixed by creating a dummy ALSA device or by removing ~/.Skype/shared.xml. See https://bbs.archlinux.org/viewtopic.php?pid=819500#p819500 for more information.

Skype can only see PulseAudio, but not ALSA devices

Turn PulseAudio autospawn off and kill PulseAudio:

$ echo "autospawn = no" > ~/.pulse/client.conf
$ killall pulseaudio

And restart Skype.

Crackling / Noisy sound (mainly using 64-bit OS)

Edit /etc/pulse/default.pa and change the following line

load-module module-udev-detect

to

load-module module-udev-detect tsched=0

See also: PulseAudio#Glitches, skips or crackling.

Problem with Audio Playback on x86_64

See Pulseaudio#Skype (x86_64 only), even if you are not using PulseAudio.

Skype sounds stops media player or other sound sources

You can try commenting out the following modules in /etc/pulse/default.pa

#module-cork-music-on-phone
#module-role-cork

If that does not help, you can try changing flat-volumes to no in /etc/pulse/daemon.conf.

flat-volumes = no