Por que esta página man tem a data de hoje?

Question

Por que uma página man específica (no meu caso, para o comando nc ) tem a data de hoje sem que eu faça nenhuma atualização no sistema? Além disso, por que o log da "atualização não assistida" não mostra nenhuma atividade específica para esse dia?

2018-03-14 07:47:38,124 INFO Initial blacklisted packages:
2018-03-14 07:47:38,135 INFO Starting unattended upgrades script
2018-03-14 07:47:38,135 INFO Allowed origins are: ['o=LinuxMint,a=qiana-security', 'o=LinuxMintESM,a=qiana']
2018-03-14 07:47:51,767 INFO No packages found that can be upgraded unattended and no pending auto-removals

Este é o rodapé da página nc man:

BSD                             March 14, 2018                             BSD

Isso é no Linux Mint 17 (qiana), baseado no Ubuntu 14.04 (trusty) com o groff 1.22.2 e man-db 2.6.7.1.

EDITAR

Saídas de comandos solicitadas:

1. man -aw nc

   /usr/share/man/man1/nc_openbsd.1.gz
   

2. ls -ld $(man -aw nc)

   -rw-r--r-- 1 root root 5.7K Dec  4  2012 /usr/share/man/man1/nc_openbsd.1.gz
   

O que é estranho ...

3. dpkg -S $(man -aw nc) ?

   netcat-openbsd: /usr/share/man/man1/nc_openbsd.1.gz
   

4. type -a man

   man is /usr/bin/man
   

5. zgrep docdate $(man -aw nc)

   .Dd $Mdocdate: February 7 2012 $
   

6. RODADA ADICIONADA strace -f man nc 2>&1 | grep -e '^BSD' -e '"/.*nc'

   ychaouche#ychaouche-PC 14:31:15 ~ $ strace -f man nc 2>&1 | grep -e '^BSD' -e '"/.*nc'
   execve("/usr/bin/man", ["man", "nc"], [/* 87 vars */]) = 0
   lstat("/usr/share/man/man1/nc.1.gz", {st_mode=S_IFLNK|0777, st_size=25, ...}) = 0
   lstat("/usr/share/man/man1/nc.1.gz", {st_mode=S_IFLNK|0777, st_size=25, ...}) = 0
   readlink("/usr/share/man/man1/nc.1.gz", "/etc/alternatives/nc.1.gz", 4095) = 25
   lstat("/etc/alternatives/nc.1.gz", {st_mode=S_IFLNK|0777, st_size=35, ...}) = 0
   readlink("/etc/alternatives/nc.1.gz", "/usr/share/man/man1/nc_openbsd.1"..., 4095) = 35
   lstat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   stat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   stat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   open("/usr/share/man/man1/nc_openbsd.1.gz", O_RDONLY) = 3
   access("/usr/share/man/man1/nc.1.gz", R_OK) = 0
   lstat("/usr/share/man/man1/nc.1.gz", {st_mode=S_IFLNK|0777, st_size=25, ...}) = 0
   lstat("/usr/share/man/man1/nc.1.gz", {st_mode=S_IFLNK|0777, st_size=25, ...}) = 0
   readlink("/usr/share/man/man1/nc.1.gz", "/etc/alternatives/nc.1.gz", 4095) = 25
   lstat("/etc/alternatives/nc.1.gz", {st_mode=S_IFLNK|0777, st_size=35, ...}) = 0
   readlink("/etc/alternatives/nc.1.gz", "/usr/share/man/man1/nc_openbsd.1"..., 4095) = 35
   lstat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   stat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   stat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   open("/usr/share/man/man1/nc_openbsd.1.gz", O_RDONLY) = 3
   stat("/usr/share/man/man1/nc.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   stat("/usr/share/man/cat1/nc.1.gz", 0x7fffa49c0940) = -1 ENOENT (No such file or directory)
   stat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   open("/usr/share/man/man1/nc_openbsd.1.gz", O_RDONLY) = 3
   [pid  3878] stat("/usr/share/man/man1/nc_openbsd.1.gz", {st_mode=S_IFREG|0644, st_size=5756, ...}) = 0
   [pid  3878] access("/usr/share/man/man1/nc_openbsd.1.gz", R_OK <unfinished ...>
   BSD                             March 20, 2018                             BSD
   

7. strace -f man nc 2>&1 | grep -vwe -1 | grep -o '"/[^"]*"' | sort -u | grep -v /dev/ | xargs sh -c 'zgrep "March 14" "$@"' sh 2> /dev/null

    no output
   

   parece que a data não está codificada. Pode ser uma macro gerando a data de hoje.

8. env | grep -e ROFF -e MAN -e GRO

   SESSION_MANAGER=local/ychaouche-PC:@/tmp/.ICE-unix/2915,unix/ychaouche-PC:/tmp/.ICE-unix/2915
   MANDATORY_PATH=/usr/share/gconf/default.mandatory.path
   

9. env -i man nc mostra a data de hoje (20 de março de 2018)

10. zcat /usr/share/man/man1/nc_openbsd.1.gz | nroff -mandoc | grep BSD

    ychaouche#ychaouche-PC 06:59:53 ~ $ zcat /usr/share/man/man1/nc_openbsd.1.gz | nroff -mandoc | grep BSD
    NC(1)                     BSD General Commands Manual                    NC(1)
    BSD                             March 20, 2018                             BSD
    ychaouche#ychaouche-PC 07:01:41 ~ $
    

11. strace -f man nc 2>&1 | grep -vwe -1 | grep -o '"/[^"]*tmac/[^"]*"' | sort -u | xargs ls -lrtd

    ychaouche#ychaouche-PC 17:26:08 /usr/share/man/man1 $ unalias ls
    ychaouche#ychaouche-PC 17:26:12 /usr/share/man/man1 $ unalias xargs
    ychaouche#ychaouche-PC 17:26:14 /usr/share/man/man1 $ unalias grep
    ychaouche#ychaouche-PC 17:26:16 /usr/share/man/man1 $ strace -f man nc 2>&1 | grep -vwe -1 | grep -o '"/[^"]*tmac/[^"]*"' | sort -u | xargs ls -lrtd
    -rw-r--r-- 1 root root  4065 Jan 22  2014 /usr/share/groff/1.22.2/tmac/papersize.tmac
    -rw-r--r-- 1 root root  1860 Jan 22  2014 /usr/share/groff/1.22.2/tmac/andoc.tmac
    -rw-r--r-- 1 root root    71 Jan 22  2014 /usr/share/groff/1.22.2/tmac/unicode.tmac
    -rw-r--r-- 1 root root  1552 Jan 22  2014 /usr/share/groff/1.22.2/tmac/tty.tmac
    -rw-r--r-- 1 root root  5183 Jan 22  2014 /usr/share/groff/1.22.2/tmac/tty-char.tmac
    -rw-r--r-- 1 root root  1145 Jan 22  2014 /usr/share/groff/1.22.2/tmac/troffrc-end
    -rw-r--r-- 1 root root  1387 Jan 22  2014 /usr/share/groff/1.22.2/tmac/troffrc
    -rw-r--r-- 1 root root  4729 Jan 22  2014 /usr/share/groff/1.22.2/tmac/pspic.tmac
    -rw-r--r-- 1 root root 22042 Jan 22  2014 /usr/share/groff/1.22.2/tmac/mdoc/doc-syms
    -rw-r--r-- 1 root root  4048 Jan 22  2014 /usr/share/groff/1.22.2/tmac/mdoc/doc-nroff
    -rw-r--r-- 1 root root 29284 Jan 22  2014 /usr/share/groff/1.22.2/tmac/mdoc/doc-common
    -rw-r--r-- 1 root root  2250 Jan 22  2014 /usr/share/groff/1.22.2/tmac/latin1.tmac
    -rw-r--r-- 1 root root 27860 Jan 22  2014 /usr/share/groff/1.22.2/tmac/hyphen.us
    -rw-r--r-- 1 root root 15678 Jan 22  2014 /usr/share/groff/1.22.2/tmac/hyphenex.us
    -rw-r--r-- 1 root root  1362 Jan 22  2014 /usr/share/groff/1.22.2/tmac/fallbacks.tmac
    -rw-r--r-- 1 root root 73807 Jan 22  2014 /usr/share/groff/1.22.2/tmac/doc.tmac
    -rw-r--r-- 1 root root   537 Jan 22  2014 /usr/share/groff/1.22.2/tmac/composite.tmac
    -rw-r--r-- 1 root root   704 Jan 22  2014 /usr/share/groff/site-tmac/mdoc.local
    ychaouche#ychaouche-PC 17:26:18 /usr/share/man/man1 $
    

Answer 1

O GNU roff não costumava suportar isso:

 .Dd $Mdocdate: February 7 2012 $

Extensão OpenBSD (aqui que $Mdocdate: ...$ é uma palavra-chave CVS / RCS expandida pelo CVS (que o OpenBSD usa para controlar seu código na versão) com a data da revisão manual), resultando na data atual a ser expandida em vez da um especificado. Eu posso reproduzi-lo no Ubuntu 14.04 para todas as páginas man que possuem um Mdocdate .

Veja o link implementado em link (versão 1.22.3 do groff).

Para páginas man do MirBSD (agora MirOS) como seu paxcpio ou mksh , que usam a mesma palavra-chave $Mdocdate: ...$ CVS, você encontrará as páginas man redefinindo (wrap) a própria macro .Dd mdoc , então as macros do sistema roff não precisam suportá-lo:

.\"
.\" Implement .Dd with the Mdocdate RCS keyword
.\"
.rn Dd xD
.de Dd
.ie ^G\$1^G$Mdocdate:^G \{\
.       xD \$2 \$3, \$4
.\}
.el .xD \$1 \$2 \$3 \$4 \$5 \$6 \$7 \$8
..
.\"
.\" .Dd must come before definition of .Mx, because when called
.\" with -mandoc, it might implement .Mx itself, but we want to
.\" use our own definition. And .Dd must come *first*, always.
.\"
.Dd $Mdocdate: August 16 2017 $