How to troubleshoot suspend and hibernate in Ubuntu
Some tips are at https://wiki.ubuntu.com/DebuggingKernelSuspendHibernateResume
Fails to suspend/hibernate
$ dmesg|less
There is usually an entry what application caused the suspension to fail:
[32467.560058] Freezing of tasks failed after 20.01 seconds (1 tasks refusing to freeze, wq_busy=0):
[32467.560115] plasma-desktop D 0000000000000000 0 2065 1 0x00800004
...
The stack trace often tells you where the problem might lie:
[32467.560155] [<ffffffff81087f00>] ? autoremove_wake_function+0x0/0x40
[32467.560163] [<ffffffffa016e523>] SendReceive+0x1a3/0x3b0 [cifs]
[32467.560169] [<ffffffffa0153c79>] CIFSSMBUnixQPathInfo+0x139/0x2b0 [cifs]
[32467.560176] [<ffffffffa016853d>] cifs_get_inode_info_unix+0x7d/0x1a0
- here it is the CIFS (samba) mounts.
Fail to resume
Make sure the swap partition is correctly set, see https://help.ubuntu.com/community/SwapFaq