Mitar's questions

I have a block device (/dev/mapper/vg0-data) on a server. I am planning to mount it locally on the server directly through Linux mount, but also expose is through iSCSI to another server, which will connect to it twice to have multi-path connection. I wonder if this is OK or will there be any data corruption because there might be potentially both local changes on the server and remote changes coming from iSCSI. If there is any caching involved there might be conflicts? Should I mount also locally the block device over iSCSI?

The block device contains an ext4 partition.

This is all on Linux, Ubuntu 16.04 LTS.

I am trying to log changes to a file system using auditd, but I am seeing also many other things being logged, for example all failed SSH logging attempts (USER_AUTH and USER_LOGIN events). How can I prevent them from being logged? When I do auditctl -l I see only the path watching rules and no other rules.

The VGA port on the integrated graphical card broke off the mother board. I bought the replacement VGA card and added it to the system, hoping that the server will just use the new VGA card for its output but this does not seem to be so. How can I get the system to use the new VGA card without being able to see anything?

The new graphical card is EVGA GeForce 210. Server is an older version of this one.

I use debsums to daily check changes to installed packages on multiple servers. The issue is that some packages start reporting mismatches every so and so and even if I reinstall the package, after few days the mismatches reappear. This is happening across multiple machines and regularly. I would love to understand why is this happening and how to fix it. All that is on Ubuntu LTS 16.04.

Examples of reported changes:

/usr/lib/x86_64-linux-gnu/mesa-egl/libEGL.so.1.0.0
/usr/lib/x86_64-linux-gnu/mesa/libGL.so.1.2.0
/usr/share/man/man1/sbt.1.gz
/usr/share/doc/libkmod2/changelog.Debian.gz
/usr/lib/x86_64-linux-gnu/old.libgbm.so.1.0.0

I reported this to Ubuntu, but I did not get any response, so I would like to get to the bottom of this but I do not understand why is happening. What is changing those files?

• https://bugs.launchpad.net/ubuntu/+bug/1681129
• https://bugs.launchpad.net/ubuntu/+bug/1681126

I have a Dell PowerEdge R410 with two SAS drives connected to the SAS controller and I would like that both of them can be in the boot sequence tried to boot. I would like to use md software RAID-1 in Linux so if one disk fails, server should try to boot from the other one. But in the BIOS I see only one hard drive (the first one) in the boot sequence and also in the boot manager I have only one hard drive listed. But otherwise the second hard drive is recognized normally (it is visible in SAS controller) and also in the Linux afterwards. Only booting works only from the first hard drive.

How to use hostname and not directly IP for set_real_ip_from in Nginx? I have a reverse proxy which can change IP as it is restated (it is a Docker container), but I do not want to trust other IPs from the same range (other Docker containers). I am using skydock to keep DNS entries resolve to correct IP for a container, so is there a way to use that for set_real_ip_from instead of static IP?

We have some problems with very slow disk response on our server. I checked iostat (iostat -d -x 30) and have some problems with its interpretation:

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               1.04   396.31    6.60   57.44   382.47  3649.21    62.95    10.31  160.87   8.64  55.36
sda               6.26   391.15   16.16   62.75  1810.79  3649.22    69.19     2.97   37.66   1.79  14.13
md0               0.00     0.00    0.55    0.01    16.88     0.08    30.11     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.02    0.07     1.10     0.54    18.31     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.02    0.04     0.13     0.34     8.00     0.00    0.00   0.00   0.00
md3               0.00     0.00   29.48  453.28  2175.15  3643.46    12.05     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00    56.15    0.70   81.34    12.00  1110.03    13.68    47.56  600.17   5.23  42.89
sda               0.00    51.02    0.47   81.37     4.53  1059.38    13.00     0.32    3.95   0.69   5.64
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    1.17   47.45    16.53   379.61     8.15     0.00    0.00   0.00   0.00

First one is initial (history) statistics iostat displays, the second one is after 30 seconds.

Why is await for sdb so higher than for sda? OK, because svctm is also higher (svctm is part of await but also influences the queue length). But why, if there are in mirror? They are both exactly the same disks, smartctl does not report any problems or significant counters difference:

SDA:

Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x002f   200   200   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   145   145   021    Pre-fail  Always       -       9716
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       71
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   200   200   000    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   080   080   000    Old_age   Always       -       14623
 10 Spin_Retry_Count        0x0032   100   253   000    Old_age   Always       -       0
 11 Calibration_Retry_Count 0x0032   100   253   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       69
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       68
193 Load_Cycle_Count        0x0032   113   113   000    Old_age   Always       -       262965
194 Temperature_Celsius     0x0022   126   114   000    Old_age   Always       -       26
196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       0

SDB:

Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x002f   200   200   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   145   145   021    Pre-fail  Always       -       9708
  4 Start_Stop_Count        0x0032   100   100   000    Old_age   Always       -       67
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   200   200   000    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   080   080   000    Old_age   Always       -       14622
 10 Spin_Retry_Count        0x0032   100   253   000    Old_age   Always       -       0
 11 Calibration_Retry_Count 0x0032   100   253   000    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       65
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       63
193 Load_Cycle_Count        0x0032   113   113   000    Old_age   Always       -       261839
194 Temperature_Celsius     0x0022   128   115   000    Old_age   Always       -       24
196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       0

/etc/fstab:

proc            /proc           proc    defaults        0       0
/dev/md0        /               ext3    relatime,errors=remount-ro 0       1
/dev/md1        /var            ext3    relatime        0       2
/dev/md2        none            swap    sw              0       0
/dev/md3        /vz             ext3    relatime        0       3
/dev/hda        /media/cdrom0   udf,iso9660 user,noauto 0       0

Some measurements with iostat -d -x 2 (every two seconds) under heavy load. You can see that both disks can have longer queue and waiting time, but sda successfully reduces this, while sdb keeps having the longer waiting time. This is strange as disks are the same and it is RAID-1 (mirror).

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00    6.00     0.00  6144.00  1024.00    21.40 4545.00 166.67 100.00
sda               0.00     0.00    2.00    1.00    16.00     8.00     8.00     0.49  390.00  75.33  22.60
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    1.50    0.50    12.00     4.00     8.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00  1405.00    0.50   23.00     4.00 10632.00   452.60    18.96 1889.62  41.62  97.80
sda               0.50  1401.50    1.50   37.50   120.00 11512.00   298.26     4.29  110.00   3.13  12.20
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    2.50 1439.00   124.00 11512.00     8.07     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00  1995.50    0.00   29.00     0.00  5304.00   182.90    13.64  873.31  34.34  99.60
sda               0.50  1986.50    6.50   28.50   512.00  1664.00    62.17     0.57    7.14   1.89   6.60
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    7.00 2046.00   512.00 16368.00     8.22     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00   930.00    0.00   18.50     0.00  1192.00    64.43    92.52  859.68  54.05 100.00
sda               0.00   928.50    0.00   35.50     0.00 18192.00   512.45    51.52  701.97  28.17 100.00
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    0.00  946.50     0.00  7572.00     8.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00   16.00     0.00  8976.00   561.00    56.14 2710.38  62.50 100.00
sda               0.00     0.00    0.00   13.50     0.00  4084.00   302.52     6.26 2457.63  47.56  64.20
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00   10.00     0.00 10240.00  1024.00    33.75 4877.20 100.00 100.00
sda               0.00     0.00    0.50    0.00     4.00     0.00     8.00     0.01   16.00  16.00   0.80
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    0.50    0.00     4.00     0.00     8.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00  3245.50    1.50   31.50   208.00 12756.00   392.85    64.57 2644.30  30.24  99.80
sda               0.00  3245.00    2.00   60.50   108.00 26444.00   424.83    17.03  272.42   4.61  28.80
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    3.50 3305.50   316.00 26444.00     8.09     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00    8.00     0.00  8192.00  1024.00    74.48 2241.50 125.00 100.00
sda               0.00     0.00    0.00    1.00     0.00     8.00     8.00     0.00    0.00   0.00   0.00
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    0.00    1.00     0.00     8.00     8.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     3.00    0.00   22.50     0.00  5192.00   230.76    58.21 3204.18  44.44 100.00
sda               0.00     3.00    3.50    6.50    48.00    76.00    12.40     0.09    8.00   5.60   5.60
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    4.00   10.00    52.00    80.00     9.43     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.50  4098.50    1.50   31.50   324.00  4160.00   135.88    78.08 3401.39  30.24  99.80
sda               0.50  4084.00    2.00   32.00   216.00  8200.00   247.53    57.79   27.53  15.35  52.20
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    4.00 4173.00   536.00 33384.00     8.12     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00   20.50     0.00  9228.00   450.15    97.71 1776.78  48.78 100.00
sda               0.00     0.00    0.00   32.00     0.00 13536.00   423.00    72.55 1675.31  31.25 100.00
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00   13.00     0.00  7220.00   555.38    67.20 3830.46  76.92 100.00
sda               0.00     0.00    0.00   25.50     0.00 11652.00   456.94    38.91 4491.14  39.22 100.00
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    0.50    0.50     4.00     4.00     8.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00   11.00     0.00  5548.00   504.36    50.62 6367.45  90.91 100.00
sda               0.00     0.00    0.00    0.00     0.00     0.00     0.00     2.37    0.00   0.00 100.00
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00    7.50     0.00  6648.00   886.40    28.48 7513.07 133.33 100.00
sda               0.00     0.00    1.50    3.50    12.00    28.00     8.00     0.24  560.80  20.80  10.40
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    1.50    2.00    12.00    16.00     8.00     0.00    0.00   0.00   0.00

Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
sdb               0.00     0.00    0.00   10.00     0.00  4036.00   403.60    12.15 9193.00 100.00 100.00
sda               0.00     0.00    1.00    0.50     8.00     4.00     8.00     0.02   14.67  14.67   2.20
md0               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md1               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md2               0.00     0.00    0.00    0.00     0.00     0.00     0.00     0.00    0.00   0.00   0.00
md3               0.00     0.00    1.00    0.50     8.00     4.00     8.00     0.00    0.00   0.00   0.00

I would like to setup Django with WSGI and Apache on root (/) of the website, but I would like that Apache servers through WSGI (and Django) only those URLs which do not have corresponding file to serve directly.

For PHP I would do something like this with:

RewriteCond %{REQUEST_FILENAME} !-f

and then rewrite to some index.php or something. But how to do that with WSGI?

I am using pipe over SSH to deliver some e-mails for special processing to another server, what I have configured in master.cf.

foobar   unix    -   n   n   -   -   pipe
  flags=RF user=foobar:foobar argv=/usr/bin/ssh -T foobar@foobar /usr/local/bin/foobar ${recipient}

The problem I am having is that if this server is not available (or for some other reason SSH connection fails) whole delivery fails and sender receives message about that. What I would like is that if it fails that e-mail is put back into the queue for later retry. And only if for few days this delivery is not made that sender is notified about that. How can I configure Postfix in this way?