whether the user listed accepts messages (the SUS displays this when -T is specified), yet GNU who and BSD who both omit a number of the above options (such as -a, -b, -d, and others); GNU who instead uses -l to perform DNS lookups on hostnames listed. Output The SUS without extensions specifies that the output format is to be "implementation-defined". The XSI extension specifies a format, but notes that it is not fully specified; delimiters and field lengths are not precisely specified. Thus, the format of the output differs considerably among Unix implementations. See also List of Unix commands References External links who — manual page from GNU coreutils Multics commands Unix user management and support-related utilities Standard Unix programs Unix SUS2008 utilities Plan 9 commands