Julia Evans

Metaphors in man pages

This morning I was watching a great talk by Maggie Appleton about metaphors. In the talk, she explains the difference between a “figurative metaphor” and a “cognitive metaphor”, and references this super interesting book called Metaphors We Live By which I immediately got and started reading.

Here’s an example from “Metaphors We Live By” of a bunch of metaphors we use for ideas:

  • ideas as food: “raw facts”, “half-baked ideas”, “swallow that claim”, “spoon-feed our students”, “meaty part of the paper”, “that idea has been fermenting for years”
  • ideas as people: “the theory of relativity gave birth to an enormous number of ideas”, “whose brainchild was that”, “those ideas died off in the middle ages”, “cognitive psychology is in its infancy
  • ideas as products: “we’ve generated a lot of ideas this week”, “it needs to be refined”, “his intellectual productivity has decreased in recent years”
  • ideas as commodities: “he won’t buy that”, “that’s a worthless idea”, “she has valuable ideas”
  • ideas as resources: “he ran out of ideas”, “let’s pool our ideas”, “that idea will go a long way
  • ideas as cutting instruments: “that’s an incisive idea”, “that cuts right to the heart of the matter”, “he’s sharp
  • ideas as fashions: “that idea went out of style years ago”, “marxism is fashionable in western europe”, “berkeley is a center of avant-garde thought”, “semiotics has become quite chic

There’s a long list of more English metaphors here, including many metaphors from the book.

I was surprised that there were so many different metaphors for ideas, and that we’re using metaphors like this all the time in normal language.

let’s look for metaphors in man pages!

Okay, let’s get to the point of this blog post, which is just a small fun exploration – there aren’t going to be any Deep Programming Insights here.

I went through some of the examples of metaphors in Metaphors To Live By and grepped all the man pages on my computer for them.

processes as people

This is one of the richer categories – a lot of different man pages seem to agree that processes are people, or at least alive in some way.

  • Hangup detected on controlling terminal or death of controlling process (man 7 signal)
  • can access the local agent through the forwarded connection (man ssh_config)
  • If the exit of the process causes a process group to become orphaned (man exit)
  • If a parent process terminates, then its “zombie” children (if any) (man wait)
  • … send SIGHUP to the parent process of the client (man tmux)
  • Otherwise, it “runs” to catch up or waits (man mplayer)
  • However, Git does not (and it should not) change tags behind users back (man git-tag)
  • will listen forever for a connection (man nc_openbsd)
  • this monitor scales badly with the number of files being observed (man fswatch)
  • If you try to use the birth time of a reference file (man file)
  • a program died due to a fatal signal (man xargs)
  • protocol version in the TLS handshake (man curl)
  • it will look for a debug object at… (man valgrind)

data as food

  • “Apparently some digital cameras get indigestion if you feed them a CF card) (man mkfs)
  • “Send packets using raw ethernet frames or IP packets” (man nmap)
  • “the above example can be thought of as a maximizing repeat that must swallow everything it can” (man pcrepattern)
  • “This will allow you to feed newline-delimited name=value pairs to the script on’ (man CGI)

data as objects

  • Kill the tmux server and clients and destroy all sessions (tmux)
  • Each command will produce one block of output on standard output. (man tmux)
  • “HTTPS guarantees that the password will not travel in the clear” (man Net::SSLeay)
  • “way to pack more than one certificate into an ASN.1 structure” (man gpgsm)

processes as machines/objects

  • “This is fragile, subject to change, and thus should not be relied upon” (man ps)
  • “This is useful if you have to use broken DNS” (man aria2c)
  • “This provides good safety measures, but breaks down when” (man git-apply)
  • “debugfs is a debugging tool. It has rough edges!” (man debugfs)


There are LOTS of containers: directories, files, strings, caches, queues, buffers, etc.

  • can exploit that to get out of the chroot directory (man chroot)
  • “The file containing the RFC 4648 Section 5 base64url encoded 128-bit secret key”
  • “Keys must start with a lowercase character and contain only hyphens”
  • “just specify an empty string” (man valgrind)
  • “the cache is full and a new page that isn’t cached becomes visible” (man zathurarc)
  • “Number of table overflows(man lnstat)
  • “likely overflow the buffer” (man g++)


There are also lots of kinds of resources: bandwidth, TCP sockets, session IDs, stack space, memory, disk space.

  • This is not recommended and wastes bitrate (man bitrate)
  • corruption or lost data if the system crashes (man btree)
  • you don’t want Wget to consume the entire available bandwidth (man wget)
  • Larger values will be slower and cause x264 to consume more memory (man mplayer)
  • the resulting file can consume some disk space (man socat)
  • attempting to reuse SSL session-ID (man curl)
  • This option controls stack space reuse (man gcc)
  • Keep the TCP socket open between queries and reuse it rather than creating a new TCP socket (man dig)
  • the maximum value will easily eat up three extra gigabytes or so of memory (man valgrind)

orientation (up, down, above, below)

  • Send the escape character to the frontend (man qemu-system)
  • Note that TLS 1.3 is only supported by a subset of TLS backends (man curl)
  • This option may be useful if you are behind a router (man mplayer)
  • When a file that exists on the lower layer is renamed (man rename)
  • Several of the socket options should be handled at lower levels (man getsockopt)
  • while still performing such higher level functionality (man nmap)
  • This is the same string passed back to the front end (man sudo_plugin)
  • On Linux, futimens is a library function implemented on top of the utimensat system call (man futimens)


Limits as rooms/buildings (which have floors, and ceilings, which you hit) are kind of fun:

  • the kernel places a floor of 32 pages on this size limit (man execve)
  • This specifies a ceiling to which the process’s nice value can be raised (man getrlimit)
  • If this limit is hit the search is aborted (man gcc)
  • these libraries are used as the foundation for many of the libraries (man Glib)

money / wealth

  • This is a very expensive operation for large projects, so use it with caution (man git-log)
  • Note that since this operation is very I/O expensive (man git-filter-branch)
  • provides a rich interface for scripts to print disk layouts (man fdisk)
  • The number of times the softirq handler function terminated per second because its budget was consumed (man sar.sysstat)
  • the extra cost depends a lot on the application at hand (man valgrind)

more miscellaneous metaphors

here are some more I found that didn’t fit into any of those categories yet.

  • when a thread is created under glibc, just one big lock is used for all thread setup (man valgrind)
  • will likely drop the connection (man x11vnc)
  • on all paths from the load to the function entry (man gcc)
  • it is a very good idea to wipe filesystem signatures, data, etc. before (man cryptsetup)
  • they will be embedded into the document
  • the client should automatically follow referrals returned
  • even if there exist mappings that cover the whole address space requested (man mremap)
  • when a network interface disappears (man systemd-resolve)

we’re all using metaphors all the time

I found a lot more metaphors than I expected, and most of them are just part of how I’d normally talk about a program. Interesting!

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