The output from blkparse can be tailored for specific use - in particular, to ease parsing of output, and/or limit output fields to those the user wants to see. The data for fields which can be output include:
| Field | Description |
| Specifier | |
| a | Action, a (small) string (1 or 2 characters) - see table below for more details |
| c | CPU id |
| C | Command |
| d | RWBS field, a (small) string (1-3 characters) - see section below for more details |
| D | 7-character string containing the major and minor numbers of the event's device |
| (separated by a comma). | |
| e | Error value |
| m | Minor number of event's device. |
| M | Major number of event's device. |
| n | Number of blocks |
| N | Number of bytes |
| p | Process ID |
| P | Display packet data - series of hexadecimal values |
| s | Sequence numbers |
| S | Sector number |
| t | Time stamp (nanoseconds) |
| T | Time stamp (seconds) |
| u | Elapsed value in microseconds (-t command line option) |
| U | Payload unsigned integer |
Note that the user can optionally specify field display width, and optionally a left-aligned specifier. These precede field specifiers, with a '%' character, followed by the optional left-alignment specifer (-) followed by the width (a decimal number) and then the field.
Thus, to specify the command in a 12-character field that is left aligned:
-f "%-12C"