This appears to be an off-by-one issue when handling reads which are
smaller than the overall returned size for the table. This is easily
spotted in the read line by line mode triggered in the following test
script:
#!/bin/bash
while read l
do
echo "$l"
done </proc/net/route
Though in my tests it also triggers with cat /proc/net/route when you
have more than 8K worth of routes, occuring at the 8K boundary.
The underlying issue is that the code does not correctly take into
account the header when starting from anywhere but the beginning. This
leads us to drop the first set of entries on restart.
** Changed in: linux (Ubuntu)
Status: Confirmed => In Progress
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https://bugs.launchpad.net/bugs/1483440
Title:
odd behavior with /proc/net/route reading via sh 'read'
Status in linux package in Ubuntu:
In Progress
Bug description:
I saw some strange behavior when one of my scripts started failing to
get the data it was looking for out of /proc/net/route
$ uname -r
$ dpkg -S /boot/vmlinux-$(uname -r)
linux-image-4.1.0-3-generic: /boot/vmlinuz-4.1.0-3-generic
$ id -u
1000
$ cp /proc/net/route /tmp/route
$ diff /proc/net/route /tmp/route
$ md5sum /proc/net/route /tmp/route
4b3663ec7554cf91764106ea9dcc2ada /proc/net/route
4b3663ec7554cf91764106ea9dcc2ada /tmp/route
## just cat the file
$ cat /proc/net/route
Iface Destination Gateway Flags RefCnt Use Metric Mask MTU
Window IRTT
eth0 00000000 01A8F50A 0003 0 0 0 00000000 00 0
eth0 00A8F50A 00000000 0001 0 0 0 00F8FFFF 00 0
virbr0 007AA8C0 00000000 0001 0 0 0 00FFFFFF 00 0
## try to read it with sh while loop
$ sh -c 'while read line; do echo line: $line; done' < /proc/net/route
line: Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT
line: eth0 00A8F50A 00000000 0001 0 0 0 00F8FFFF 0 0 0
line: virbr0 007AA8C0 00000000 0001 0 0 0 00FFFFFF 0 0 0
## odd, where did the first line go?
##
## maybe its still there if we cat
$ cat /proc/net/route | sh -c 'while read line; do echo line: $line; done'
line: Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT
line: eth0 00000000 01A8F50A 0003 0 0 0 00000000 0 0 0
line: eth0 00A8F50A 00000000 0001 0 0 0 00F8FFFF 0 0 0
line: virbr0 007AA8C0 00000000 0001 0 0 0 00FFFFFF 0 0 0
## Yep, still there.
## as expected, the copied file shows sane behavior
$ sh -c 'while read line; do echo line: $line; done' < /tmp/route
line: Iface Destination Gateway Flags RefCnt Use Metric Mask MTU Window IRTT
line: eth0 00000000 01A8F50A 0003 0 0 0 00000000 0 0 0
line: eth0 00A8F50A 00000000 0001 0 0 0 00F8FFFF 0 0 0
line: virbr0 007AA8C0 00000000 0001 0 0 0 00FFFFFF 0 0 0
ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: linux-image-4.1.0-3-generic 4.1.0-3.3
ProcVersionSignature: User Name 4.1.0-3.3-generic 4.1.3
Uname: Linux 4.1.0-3-generic x86_64
AlsaDevices:
total 0
crw-rw---- 1 root audio 116, 1 Aug 10 23:52 seq
crw-rw---- 1 root audio 116, 33 Aug 10 23:52 timer
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.18-0ubuntu6
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/seq',
'/dev/snd/timer'] failed with exit code 1:
Date: Mon Aug 10 23:55:09 2015
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
MachineType: HP ProLiant DL360 Gen9
PciMultimedia:
ProcEnviron:
TERM=xterm-256color
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcFB: 0 EFI VGA
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.1.0-3-generic
root=UUID=ebea97f1-7014-4fac-bc87-c8ff465c566f ro --- console=ttyS1,115200
RelatedPackageVersions:
linux-restricted-modules-4.1.0-3-generic N/A
linux-backports-modules-4.1.0-3-generic N/A
linux-firmware 1.146
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
SourcePackage: linux
UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 03/05/2015
dmi.bios.vendor: HP
dmi.bios.version: P89
dmi.chassis.type: 23
dmi.chassis.vendor: HP
dmi.modalias:
dmi:bvnHP:bvrP89:bd03/05/2015:svnHP:pnProLiantDL360Gen9:pvr:cvnHP:ct23:cvr:
dmi.product.name: ProLiant DL360 Gen9
dmi.sys.vendor: HP
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