I am unable to run qemu-system-x86_64 and qemu-system-i386. It seems that the system is missing libaio.so.1. ldd returns:
ldd /usr/bin/qemu-system-x86_64
linux-vdso.so.1 (0x00007fffa9e3f000)
libseccomp.so.2 => /lib/x86_64-linux-gnu/libseccomp.so.2 (0x00007fc9a378d000)
libSDL-1.2.so.0 => /usr/lib/x86_64-linux-gnu/libSDL-1.2.so.0 (0x00007fc9a34f5000)
libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007fc9a31bc000)
libasound.so.2 => /usr/lib/x86_64-linux-gnu/libasound.so.2 (0x00007fc9a2eb4000)
libpulse.so.0 => /usr/lib/x86_64-linux-gnu/libpulse.so.0 (0x00007fc9a2c64000)
libbrlapi.so.0.6 => /lib/x86_64-linux-gnu/libbrlapi.so.0.6 (0x00007fc9a2a58000)
libcacard.so.0 => /usr/lib/x86_64-linux-gnu/libcacard.so.0 (0x00007fc9a284d000)
libusbredirparser.so.1 => /usr/lib/x86_64-linux-gnu/libusbredirparser.so.1 (0x00007fc9a2645000)
libusb-1.0.so.0 => /lib/x86_64-linux-gnu/libusb-1.0.so.0 (0x00007fc9a242d000)
librdmacm.so.1 => /usr/lib/x86_64-linux-gnu/librdmacm.so.1 (0x00007fc9a2217000)
libibverbs.so.1 => /usr/lib/x86_64-linux-gnu/libibverbs.so.1 (0x00007fc9a2001000)
libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007fc9a1de4000)
libaio.so.1 => not found
libpixman-1.so.0 => /usr/lib/x86_64-linux-gnu/libpixman-1.so.0 (0x00007fc9a1b3f000)
libutil.so.1 => /lib/x86_64-linux-gnu/libutil.so.1 (0x00007fc9a193c000)
libnuma.so.1 => /usr/lib/x86_64-linux-gnu/libnuma.so.1 (0x00007fc9a1731000)
libbluetooth.so.3 => /usr/lib/x86_64-linux-gnu/libbluetooth.so.3 (0x00007fc9a150e000)
libncursesw.so.5 => /lib/x86_64-linux-gnu/libncursesw.so.5 (0x00007fc9a12df000)
libtinfo.so.5 => /lib/x86_64-linux-gnu/libtinfo.so.5 (0x00007fc9a10b5000)
libpng16.so.16 => /usr/lib/x86_64-linux-gnu/libpng16.so.16 (0x00007fc9a0e83000)
libjpeg.so.8 => /usr/lib/x86_64-linux-gnu/libjpeg.so.8 (0x00007fc9a0c1b000)
libsasl2.so.2 => /usr/lib/x86_64-linux-gnu/libsasl2.so.2 (0x00007fc9a0a00000)
libnettle.so.6 => /usr/lib/x86_64-linux-gnu/libnettle.so.6 (0x00007fc9a07ca000)
libgnutls.so.30 => /usr/lib/x86_64-linux-gnu/libgnutls.so.30 (0x00007fc9a0465000)
libxenctrl-4.9.so => /usr/lib/x86_64-linux-gnu/libxenctrl-4.9.so (0x00007fc9a0239000)
libxenstore.so.3.0 => /usr/lib/x86_64-linux-gnu/libxenstore.so.3.0 (0x00007fc9a002f000)
libxenforeignmemory-4.9.so.1 => /usr/lib/x86_64-linux-gnu/libxenforeignmemory-4.9.so.1 (0x00007fc99fe2c000)
libxengnttab-4.9.so.1 => /usr/lib/x86_64-linux-gnu/libxengnttab-4.9.so.1 (0x00007fc99fc29000)
libxenevtchn-4.9.so.1 => /usr/lib/x86_64-linux-gnu/libxenevtchn-4.9.so.1 (0x00007fc99fa26000)
libxendevicemodel-4.9.so.1 => /usr/lib/x86_64-linux-gnu/libxendevicemodel-4.9.so.1 (0x00007fc99f822000)
libfdt.so.1 => /usr/lib/x86_64-linux-gnu/libfdt.so.1 (0x00007fc99f61a000)
libspice-server.so.1 => /usr/lib/x86_64-linux-gnu/libspice-server.so.1 (0x00007fc99f2eb000)
libgmodule-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgmodule-2.0.so.0 (0x00007fc99f0e7000)
libglib-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007fc99edd1000)
librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007fc99ebc9000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fc99e82b000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fc99e613000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fc99e3f4000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fc99e003000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fc99ddff000)
libpulse-simple.so.0 => /usr/lib/x86_64-linux-gnu/libpulse-simple.so.0 (0x00007fc99dbfa000)
libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007fc99d9e8000)
libcaca.so.0 => /usr/lib/x86_64-linux-gnu/libcaca.so.0 (0x00007fc99d71f000)
libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007fc99d4f7000)
/lib64/ld-linux-x86-64.so.2 (0x00007fc9a4b50000)
libpulsecommon-11.1.so => /usr/lib/x86_64-linux-gnu/pulseaudio/libpulsecommon-11.1.so (0x00007fc99d279000)
libdbus-1.so.3 => /lib/x86_64-linux-gnu/libdbus-1.so.3 (0x00007fc99d02c000)
libnss3.so => /usr/lib/x86_64-linux-gnu/libnss3.so (0x00007fc99cce8000)
libnspr4.so => /usr/lib/x86_64-linux-gnu/libnspr4.so (0x00007fc99caab000)
libudev.so.1 => /lib/x86_64-linux-gnu/libudev.so.1 (0x00007fc99c88d000)
libnl-route-3.so.200 => /usr/lib/x86_64-linux-gnu/libnl-route-3.so.200 (0x00007fc99c618000)
libnl-3.so.200 => /lib/x86_64-linux-gnu/libnl-3.so.200 (0x00007fc99c3f8000)
libp11-kit.so.0 => /usr/lib/x86_64-linux-gnu/libp11-kit.so.0 (0x00007fc99c0c9000)
libidn2.so.0 => /usr/lib/x86_64-linux-gnu/libidn2.so.0 (0x00007fc99beac000)
libunistring.so.2 => /usr/lib/x86_64-linux-gnu/libunistring.so.2 (0x00007fc99bb2e000)
libtasn1.so.6 => /usr/lib/x86_64-linux-gnu/libtasn1.so.6 (0x00007fc99b91b000)
libhogweed.so.4 => /usr/lib/x86_64-linux-gnu/libhogweed.so.4 (0x00007fc99b6e7000)
libgmp.so.10 => /usr/lib/x86_64-linux-gnu/libgmp.so.10 (0x00007fc99b466000)
libxentoollog-4.9.so.1 => /usr/lib/x86_64-linux-gnu/libxentoollog-4.9.so.1 (0x00007fc99b263000)
libxencall-4.9.so.1 => /usr/lib/x86_64-linux-gnu/libxencall-4.9.so.1 (0x00007fc99b060000)
libopus.so.0 => /usr/lib/x86_64-linux-gnu/libopus.so.0 (0x00007fc99ae16000)
libgio-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0 (0x00007fc99aa78000)
liblz4.so.1 => /usr/lib/x86_64-linux-gnu/liblz4.so.1 (0x00007fc99a85c000)
libgstapp-1.0.so.0 => /usr/lib/x86_64-linux-gnu/libgstapp-1.0.so.0 (0x00007fc99a64d000)
libgstreamer-1.0.so.0 => /usr/lib/x86_64-linux-gnu/libgstreamer-1.0.so.0 (0x00007fc99a313000)
libgobject-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgobject-2.0.so.0 (0x00007fc99a0bf000)
libssl.so.1.1 => /usr/lib/x86_64-linux-gnu/libssl.so.1.1 (0x00007fc999e55000)
libcrypto.so.1.1 => /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1 (0x00007fc9999dd000)
liborc-0.4.so.0 => /usr/lib/x86_64-linux-gnu/liborc-0.4.so.0 (0x00007fc999761000)
libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007fc9994ef000)
libslang.so.2 => /lib/x86_64-linux-gnu/libslang.so.2 (0x00007fc99900d000)
libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007fc998e09000)
libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007fc998c03000)
libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x00007fc99897f000)
libwrap.so.0 => /lib/x86_64-linux-gnu/libwrap.so.0 (0x00007fc998775000)
libsndfile.so.1 => /usr/lib/x86_64-linux-gnu/libsndfile.so.1 (0x00007fc9984fc000)
libasyncns.so.0 => /usr/lib/x86_64-linux-gnu/libasyncns.so.0 (0x00007fc9982f6000)
libnssutil3.so => /usr/lib/x86_64-linux-gnu/libnssutil3.so (0x00007fc9980c7000)
libplc4.so => /usr/lib/x86_64-linux-gnu/libplc4.so (0x00007fc997ec2000)
libplds4.so => /usr/lib/x86_64-linux-gnu/libplds4.so (0x00007fc997cbe000)
libffi.so.6 => /usr/lib/x86_64-linux-gnu/libffi.so.6 (0x00007fc997ab6000)
libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007fc99788e000)
libresolv.so.2 => /lib/x86_64-linux-gnu/libresolv.so.2 (0x00007fc997673000)
libmount.so.1 => /lib/x86_64-linux-gnu/libmount.so.1 (0x00007fc99741f000)
libgstbase-1.0.so.0 => /usr/lib/x86_64-linux-gnu/libgstbase-1.0.so.0 (0x00007fc9971ab000)
libbsd.so.0 => /lib/x86_64-linux-gnu/libbsd.so.0 (0x00007fc996f96000)
liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007fc996d70000)
libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x00007fc996a55000)
libnsl.so.1 => /lib/x86_64-linux-gnu/libnsl.so.1 (0x00007fc99683b000)
libFLAC.so.8 => /usr/lib/x86_64-linux-gnu/libFLAC.so.8 (0x00007fc9965c4000)
libogg.so.0 => /usr/lib/x86_64-linux-gnu/libogg.so.0 (0x00007fc9963bb000)
libvorbis.so.0 => /usr/lib/x86_64-linux-gnu/libvorbis.so.0 (0x00007fc996190000)
libvorbisenc.so.2 => /usr/lib/x86_64-linux-gnu/libvorbisenc.so.2 (0x00007fc995ee7000)
libblkid.so.1 => /lib/x86_64-linux-gnu/libblkid.so.1 (0x00007fc995c9a000)
libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x00007fc995a85000)
libuuid.so.1 => /lib/x86_64-linux-gnu/libuuid.so.1 (0x00007fc99587e000)
However it looks to me as if that library is installed correctly:
dpkg -l libaio*
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-============================-===================-===================-=============================================================
ii libaio1:amd64 0.3.110-5 amd64 Linux kernel AIO access library - shared library
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: qemu-system-x86 1:2.11+dfsg-1ubuntu7
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Mon May 14 15:06:27 2018
InstallationDate: Installed on 2018-04-27 (16 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
KvmCmdLine: COMMAND STAT EUID RUID PID PPID %CPU COMMAND
MachineType: VMware, Inc. VMware Virtual Platform
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no username)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-20-generic root=UUID=5f8e37ed-165c-4faf-9ccb-17bacfc7d5b8 ro find_preseed=/preseed.cfg auto noprompt priority=critical locale=en_US quiet
SourcePackage: qemu
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 05/19/2017
dmi.bios.vendor: Phoenix Technologies LTD
dmi.bios.version: 6.00
dmi.board.name: 440BX Desktop Reference Platform
dmi.board.vendor: Intel Corporation
dmi.board.version: None
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 1
dmi.chassis.vendor: No Enclosure
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnPhoenixTechnologiesLTD:bvr6.00:bd05/19/2017:svnVMware,Inc.:pnVMwareVirtualPlatform:pvrNone:rvnIntelCorporation:rn440BXDesktopReferencePlatform:rvrNone:cvnNoEnclosure:ct1:cvrN/A:
dmi.product.name: VMware Virtual Platform
dmi.product.version: None
dmi.sys.vendor: VMware, Inc.
Update: Re-installing the package solved the problem. I can't tell why the files where not present - the installation was brand-new.