popup says "backup is already running", but it isn't

[Timothy F. Havel]

Opening "deja-dup-preferences", setting up backup and clicking "Backup Now" reliably results in a "Backup is already running" popup. deja-dup-monitor is running in the background, but it is automatically launched on startup and so is presumably only needed for automatic backups, which I haven't scheduled yet. Doing a "tail -f /var/log/messages" shows permission to a socket is being denied, which results a "Failed to connect to proxy" message, although I've asked deja-dup-preferences to backup to a USB SSD, not over the network. Can't figure this one out on my own.

Reporting guidelines:

$ lsb_release -d
Description: CentOS Linux release 7.3.1611 (Core)

$ rpm -q deja-dup duplicity
deja-dup-34.3-1.el7.x86_64
duplicity-0.7.12-1.el7.x86_64

$ /usr/bin/gsettings list-recursively org.gnome.DejaDup > /tmp/deja-dup.gsettings
$ cat !$
cat /tmp/deja-dup.gsettings
org.gnome.DejaDup last-restore ''
org.gnome.DejaDup periodic false
org.gnome.DejaDup full-backup-period 90
org.gnome.DejaDup backend 'file'
org.gnome.DejaDup last-run ''
org.gnome.DejaDup nag-check ''
org.gnome.DejaDup prompt-check '2017-06-06T20:11:50.742779Z'
org.gnome.DejaDup root-prompt true
org.gnome.DejaDup include-list ['$HOME']
org.gnome.DejaDup exclude-list ['$TRASH', '$DOWNLOAD']
org.gnome.DejaDup last-backup ''
org.gnome.DejaDup periodic-period 7
org.gnome.DejaDup delete-after 0
org.gnome.DejaDup.S3 id ''
org.gnome.DejaDup.S3 bucket ''
org.gnome.DejaDup.S3 folder 'captain-nemo'
org.gnome.DejaDup.OpenStack authurl ''
org.gnome.DejaDup.OpenStack tenant ''
org.gnome.DejaDup.OpenStack username ''
org.gnome.DejaDup.OpenStack container 'captain-nemo'
org.gnome.DejaDup.GCS id ''
org.gnome.DejaDup.GCS bucket ''
org.gnome.DejaDup.GCS folder 'captain-nemo'
org.gnome.DejaDup.GDrive email ''
org.gnome.DejaDup.GDrive folder '/deja-dup/captain-nemo'
org.gnome.DejaDup.Rackspace username ''
org.gnome.DejaDup.Rackspace container 'captain-nemo'
org.gnome.DejaDup.File path 'file:///media/veracrypt1/timfh'
org.gnome.DejaDup.File short-name '500 GB Volume'
org.gnome.DejaDup.File uuid '33b45c2e-fc0d-4085-b34f-187e6061fcb1'
org.gnome.DejaDup.File icon '. GThemedIcon drive-removable-media drive-removable drive'
org.gnome.DejaDup.File relpath b'timfh'
org.gnome.DejaDup.File name '500 GB Volume'
org.gnome.DejaDup.File type 'normal'

$ DEJA_DUP_DEBUG=1 deja-dup --backup | tail -n 1000

(deja-dup:6116): libnotify-WARNING **: Failed to connect to proxy