ubuntu – 以root身份ping不能与主机名一起使用,但是使用ip,普通用户可以正常工作

从ubuntu 12.04升级后,我遇到了一个奇怪的ping问题.到14.04.
我无法使用主机名ping,但使用ip它可以正常运行.我没有其他服务或程序的任何其他DNS问题.
我作为普通用户工作,但不是root用户.
作为root用户主机和dig可以将dnsname解析为ip.
busybox ping也适用于主机名.

这是错误：

root@myhost:~# ping ubuntu.com
ping: unknown host ubuntu.com

这有效：

root@myhost:~# host ubuntu.com
ubuntu.com has address 91.189.94.40
ubuntu.com mail is handled by 10 mx.canonical.com.


root@myhost:~# ping 91.189.94.40 -c 1
PING 91.189.94.40 (91.189.94.40) 56(84) bytes of data.
64 bytes from 91.189.94.40: icmp_seq=1 ttl=53 time=16.1 ms


root@myhost:~# busybox ping ubuntu.com -c 1
PING ubuntu.com (91.189.94.40): 56 data bytes
64 bytes from 91.189.94.40: seq=0 ttl=53 time=16.189 ms


user@myhost:~$ping ubuntu.com -c 1
PING ubuntu.com (91.189.94.40) 56(84) bytes of data.
64 bytes from ovinnik.canonical.com (91.189.94.40): icmp_seq=1 ttl=53 time=16.1 ms

文件/etc/nsswitch.conf

root@myhost:~# cat /etc/nsswitch.conf
# /etc/nsswitch.conf
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed,try:
# `info libc "Name Service Switch"' for information about this file.


passwd:         compat
group:          compat
shadow:         compat


hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4
networks:       files


protocols:      db files
services:       db files
ethers:         db files
rpc:            db files


netgroup:       nis

一些额外的信息.谢谢strace tip. appamor不活跃.

strace：打开/etc/resolv.conf似乎是个问题,但是根本不行

root@myhost:~# strace -e open ping -c 1 ubuntu.com
open("/etc/ld.so.cache",O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libcap.so.2",O_RDONLY|O_CLOEXEC) = 3
open("/lib/x86_64-linux-gnu/libc.so.6",O_RDONLY|O_CLOEXEC) = 3
open("/etc/resolv.conf",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/etc/nsswitch.conf",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/etc/ld.so.cache",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/x86_64-linux-gnu/tls/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/x86_64-linux-gnu/tls/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/x86_64-linux-gnu/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/x86_64-linux-gnu/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/x86_64-linux-gnu/tls/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/x86_64-linux-gnu/tls/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/x86_64-linux-gnu/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/x86_64-linux-gnu/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/tls/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/tls/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/lib/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/tls/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/tls/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/x86_64/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
open("/usr/lib/libnss_dns.so.2",O_RDONLY|O_CLOEXEC) = -1 EACCES (Permission denied)
ping: unknown host ubuntu.com
+++ exited with 2 +++

getent：

root @ myhost：〜#getent hosts ubuntu.com
91.189.94.40 ubuntu.com

getcap：

root@myhost:~# getcap -rv /bin/ping
/bin/ping

权限：

root@myhost:/etc# ls -lha /etc/resolv.conf
lrwxrwxrwx 1 root root 29 Jan  9 11:11 /etc/resolv.conf -> ../run/resolvconf/resolv.conf
root@myhost:/etc# ls -lha /run/resolvconf/resolv.conf
-rw-r--r-- 1 root root 237 Jan 10 08:52 /run/resolvconf/resolv.conf
root@myhost:/etc# ls -lha /etc/hosts
-rw-r--r-- 1 root root 485 Jan  8 09:15 /etc/hosts
root@myhost:/etc# ls -lha /etc/nsswitch.conf
-rw-r--r-- 1 root root 513 Jan  8 09:08 /etc/nsswitch.conf

resolv.conf :(与另一台主机相同,是否有效)

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 213.133.98.98
nameserver 213.133.99.99
nameserver 213.133.100.100

strace输出显示,在ping丢弃权限的位置,它会在每次打开的调用中开始获取EACCES错误.这表明权限问题是根本原因.

由于/ etc,/ lib和/ usr之间的路径都受到问题的影响,因此要检查的最明显的事情是/上的权限.这是他们在健康的Ubuntu 14.04系统上的样子：

$ls -ld /
drwxr-xr-x 23 root root 4096 Jan  7 16:55 /

在您的情况下,所有者缺少x权限

drw-r-xr-x 26 root root 4096 Dec 30 23:09 /

此特定情况将导致特定情况下的问题,其中进程已删除访问文件系统中的任何文件但保留用户标识0的功能.