I have recently installed mono 3.2.8 and monodevelop 4 from the Ubuntu 14.04 software centre. However, when I try to run monodevelop from the dash menu, nothing happens - due to this, I tried to run it from the terminal and it said "The assembly mscorlib.dll was not found or could not be loaded. It should have been installed in the /usr/lib/mono/4.5/mscorlib.dll directory." How do I fix this? I have already trie a variety of things that do not work. I have already tried running the following commands:

sudo apt-get install mono-complete
sudo apt-get install mono-devel
sudo apt-get install mono-gmcs
sudo apt-get install mono-dmcs
sudo apt-get install libmono-system.data2.0-cil
sudo apt-get install libmono-system2.0-cil
sudo apt-get install libmono2.0-cil
sudo apt-get install --reinstall monodevelop
sudo apt-get install --reinstall mono-runtime

None of these worked. What shall I do?


Now, I installed libmono-corlib4.0-cil and libmono-corlib4.5-cil, and that problem has been fixed. However, a new message has now appeared:

Missing method .ctor in assembly /usr/lib/monodevelop/bin/MonoDevelop.Ide.dll, type     System.Runtime.CompilerServices.ExtensionAttribute
Can't find custom attr constructor image: /usr/lib/monodevelop/bin/MonoDevelop.Ide.dll         mtoken: 0x0a000910
* Assertion at class.c:5597, condition `!mono_loader_get_last_error ()' not met


  at <unknown> <0xffffffff>
  at MonoDevelop.Startup.MonoDevelopMain.Main (string[]) <IL 0x00001, 0x00013>
  at (wrapper runtime-invoke) <Module>.runtime_invoke_int_object     (object,intptr,intptr,intptr) <IL 0x0005c, 0xffffffff>

Native stacktrace:

monodevelop() [0x8105b4a]
/lib/i386-linux-gnu/libc.so.6(gsignal+0x47) [0xb74de937]
/lib/i386-linux-gnu/libc.so.6(abort+0x143) [0xb74e1d63]
monodevelop() [0x8288b23]
monodevelop() [0x8288bb3]
monodevelop() [0x816b4d1]
monodevelop(mono_class_get_full+0xff) [0x816bdff]
monodevelop(mono_class_from_name+0x107) [0x816c237]
monodevelop(mono_class_from_typeref+0x190) [0x816b9a0]
monodevelop(mono_class_get_full+0x164) [0x816be64]
monodevelop(mono_class_get+0x1f) [0x816bf4f]
monodevelop(mono_metadata_parse_mh_full+0x45c) [0x81b29fc]
monodevelop(mono_method_get_header+0xbf) [0x819130f]
monodevelop() [0x807ff7c]
monodevelop() [0x8066ccc]
monodevelop() [0x8068de4]
monodevelop() [0x8069aee]
monodevelop() [0x8106d17]
monodevelop() [0x8069bf0]

Debug info from gdb:

Could not attach to process.  If your uid matches the uid of the target
process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try
again as the root user.  For more details, see /etc/sysctl.d/10-ptrace.conf
ptrace: Operation not permitted.
No threads.

Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries 
used by your application.

1 Answer 1


That file is provided by libmono-corlib4.5-cil. Install it:

sudo apt-get install libmono-corlib4.5-cil
  • Thanks Muru! However, There is a new error message which I have posted as an edit to my original question.
    – buffalo
    Aug 15, 2014 at 11:11

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