Public bug reported:

When building a disk image inside a docker container an `apt-get update`
executed in the chroot filesystem is very slow.  This seems similar to
behaviour reported in #1332440.

Ubuntu bionic host docker-ce 5:18.09.1~3-0~ubuntu-bionic -> ubuntu:18.04
docker image -> bionic chroot in filesystem


This is the strace log for `time chroot /chroot strace -f -c apt-get update`.  
Without strace the time taken is several minutes.

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 64.10 3320.491672    15736927       211           wait4
 35.80 1854.413794          41  45088937  45088461 fcntl
  0.02    1.241204          51     24449           write
  0.02    1.139271          85     13385           select
  0.02    0.812803          30     26800           rt_sigprocmask
  0.01    0.576267          38     15216       952 stat
  0.01    0.417666          31     13475           gettimeofday
  0.00    0.134767          46      2910           mmap
  0.00    0.133443          20      6515         4 read
  0.00    0.125584          56      2252           mprotect
  0.00    0.105820          48      2211       283 openat
  0.00    0.090246          32      2821        24 close
  0.00    0.058151          43      1343      1334 access
  0.00    0.056635          34      1674           fstat
  0.00    0.028297          18      1586           rt_sigaction
  0.00    0.021441          34       636           brk
  0.00    0.017399          84       208           munmap
  0.00    0.017212         233        74        32 unlink
  0.00    0.012868          55       236           getdents
  0.00    0.008162          80       102       102 statfs
  0.00    0.007709          26       293           dup2
  0.00    0.006800          32       215         4 clone
  0.00    0.006028          40       152           arch_prctl
  0.00    0.005355          35       152           execve
  0.00    0.004548          31       147           prlimit64
  0.00    0.003690          27       139           set_robust_list
  0.00    0.003585          24       151           pipe
  0.00    0.003491          32       108        16 lseek
  0.00    0.003158          34        92           set_tid_address
  0.00    0.002912          38        77           futex
  0.00    0.002291          42        55        51 ioctl
  0.00    0.002144          13       164         1 rt_sigreturn
  0.00    0.001891          33        58           getuid
  0.00    0.001825          46        40           lstat
  0.00    0.001694          17        99           geteuid
  0.00    0.001461          27        54           getpid
  0.00    0.001402          33        43           umask
  0.00    0.001380          69        20         4 unlinkat
  0.00    0.000996          13        76        44 faccessat
  0.00    0.000797          50        16         4 newfstatat
  0.00    0.000703          35        20         4 fadvise64
  0.00    0.000698         175         4           mkdir
  0.00    0.000500          50        10           chmod
  0.00    0.000469          39        12           getgid
  0.00    0.000441          55         8           lchown
  0.00    0.000405          51         8           utimensat
  0.00    0.000402          50         8           sysinfo
  0.00    0.000392          33        12           sigaltstack
  0.00    0.000380          48         8           getppid
  0.00    0.000307          20        15        13 connect
  0.00    0.000273          68         4           fchmodat
  0.00    0.000269          17        16           socket
  0.00    0.000268          34         8           flistxattr
  0.00    0.000258          65         4           sched_getaffinity
  0.00    0.000254          32         8         8 fstatfs
  0.00    0.000219          55         4           fsetxattr
  0.00    0.000209          52         4           dup
  0.00    0.000202          29         7           getegid
  0.00    0.000179          45         4           getcwd
  0.00    0.000174          44         4           fchdir
  0.00    0.000166          42         4         4 fgetxattr
  0.00    0.000159          80         2           chown
  0.00    0.000151          38         4           uname
  0.00    0.000114          38         3           setgid
  0.00    0.000105          26         4           chdir
  0.00    0.000096          24         4           setgroups
  0.00    0.000089          22         4           setresuid
  0.00    0.000081          20         4           setresgid
  0.00    0.000070          18         4           kill
  0.00    0.000039          20         2           prctl
  0.00    0.000038          38         1           getgroups
  0.00    0.000000           0         4           poll
  0.00    0.000000           0        10           mremap
  0.00    0.000000           0         3           sendto
  0.00    0.000000           0        32         7 recvfrom
  0.00    0.000000           0         6           sendmsg
  0.00    0.000000           0         2           recvmsg
  0.00    0.000000           0         1           bind
  0.00    0.000000           0         1           getsockname
  0.00    0.000000           0         1           getsockopt
  0.00    0.000000           0         2           rename
  0.00    0.000000           0         4           fchmod
  0.00    0.000000           0         2           getrusage
  0.00    0.000000           0         2           getresuid
  0.00    0.000000           0         2           getresgid
  0.00    0.000000           0         3           clock_gettime
  0.00    0.000000           0         5           getrandom
------ ----------- ----------- --------- --------- ----------------
100.00 5179.973969              45207476  45091352 total

real    133m21.564s
user    30m10.764s
sys     139m27.158s

After bind mounting /proc to the chroot from the docker container the
speed was normal.  I'm not sure if this is an edge case that doesn't
warrant attention or if it is revealing some adverse behaviour which
needs attention.  Now I know to mount /proc its not so much of a
problem.

** Affects: apt (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1815426

Title:
  slow apt-get update when no /proc

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