De man top
-b : Batch mode operation
Starts top in 'Batch mode', which could be useful for sending
output from top to other programs or to a file. In this
mode, top will not accept input and runs until the iterations
limit you've set with the '-n' command-line option or until
killed.
-H : Threads toggle
Starts top with the last remembered 'H' state reversed. When
this toggle is On, all individual threads will be displayed.
Otherwise, top displays a summation of all threads in a
process.
-n : Number of iterations limit as: -n number
Specifies the maximum number of iterations, or frames, top
should produce before ending.
-u : Monitor by user as: -u somebody
Monitor only processes with an effective UID or user name
matching that given.
Portanto, significa operar no modo de lote ( -b ), alternar a exibição do thread ( -H ), para uma única iteração ( -n 1 ), mostrando apenas os processos pertencentes ao usuário mail ( -u mail ): basicamente um instantâneo único dos encadeamentos atuais pertencentes a mail , mais ou menos equivalente a ps -Lfu mail