svn lock — Lock working copy paths or URLs in the repository, so that no other user can commit changes to them.
Lock each TARGET.  If any
            TARGET is already locked by
            another user, print a warning and continue locking the
            rest of the TARGETs.  Use
            --force to steal a lock from another user
            or working copy.
--targets ARG --message (-m) ARG --file (-F) ARG --force-log --encoding ARG --username ARG --password ARG --no-auth-cache --non-interactive --config-dir ARG --force
Lock two files in your working copy:
$ svn lock tree.jpg house.jpg 'tree.jpg' locked by user 'harry'. 'house.jpg' locked by user 'harry'.
Lock a file in your working copy that is currently locked by another user:
$ svn lock tree.jpg
svn: warning: Path '/tree.jpg is already locked by user 'harry in \
     filesystem '/svn/repos/db'
$ svn lock --force foo
'tree.jpg' locked by user 'sally'.
Lock a file without a working copy:
$ svn lock http://svn.red-bean.com/repos/test/tree.jpg 'tree.jpg' locked by user 'sally'.
For further details, see the section called “Locking”.