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I have trouble writing to external drives. They are monuted automatically in Nautilus, but I cannot copy anything there ('Paste' and 'create Folder' are just greyed out).

Does anyone have ideas what could be wrong?

The drive is named 4E29-64CA (but other drives behave the same) and I get the following error when trying to do anything to it:

/run/media/username/4E29-64CA $ touch foo
touch: cannot touch ‘foo’: Read-only file system

As root same error:

/run/media/username/4E29-64CA $ sudo touch foo
[sudo] password for username: 
touch: cannot touch ‘foo’: Read-only file system

ls -l /run/media/username gives the following:

drwx------ 6 xxxxxxxx users 4096 Jan  1  1970 4E29-64CA

So it seems I have the right permissions.

Further relevant(?) stuff:

Output of mount:

$ mount | grep 4E29
/dev/sdc1 on /run/media/username/4E29-64CA type vfat (ro,nosuid,nodev,relatime,uid=1000,gid=100,fmask=0022,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,showexec,utf8,flush,errors=remount-ro,uhelper=udisks2)
$ mount | grep 1000
tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=372244k,mode=700,uid=1000,gid=100)
gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=100)

Groups I am in:

$ groups
audio storage users networkmanager sudoers

From /usr/share/polkit-1/actions/org.freedesktop.udisks2.policy:

<action id="org.freedesktop.udisks2.filesystem-mount">
    <description>Mount a filesystem</description>
    <message>Authentication is required to mount the filesystem</message>
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First I think the problem is mounting the USB in the /run directory.

Try this:

create a mounting point on /media. Let's named myUsb

sudo mkdir /media/myUsb

Try to remount with rw permissions

sudo mount -o remount,rw /partition/identifier /mount/point

Then in your case the command will be

sudo mount -o remount,rw /dev/sdc1 /media/myUsb
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