Category:Linux troubleshooting
This category will contain a collection of articles on troubleshooting Linux. It will be highly biased towards SuSE Linux (version 10.1 or later), as that is my primary OS. I am also using a 64-bit (x86_64) kernel, so my articles will also be biased towards these systems.
Note: Most of the following have also been tested on Mandriva Linux.
Contents
System information
% dmesg % vmstat # to quickly monitor CPU, memory, and I/O usage and decide which is the bottleneck
% ps -ef | egrep '^root ' | gawk '{print $2}' # method 1 % pgrep -u root # method 2
% cat /proc/cpuinfo % cat /proc/partitions % cat /proc/meminfo % cat /proc/sys/vm/swappiness # number from 0 - 100; the higher the number the more the system will swap % cat /proc/interrupts # inspect your /proc/interrupts file for multiple devices having the same interrupt
% uname -a # system architecture % grep ^VERSION /etc/SuSE-release # To see which SuSE Linux version you are using % cat /etc/mandriva-release # To see which Mandriva Linux version you are using % pstree % lsof | grep TCP # list open files % lsof | grep ' root ' | awk '{print $NF}' | sort | uniq | wc -l # list number of open files for a user
% getconf # print system configuration variables % getconfig # get configuration information for the Xorg server % systool # view system device information by bus, class, and topology % bind -P # print keyboard bindings
% cat /proc/scsi/scsi WDC WD2000JD-22H Rev: 08.0 SATA-I, 200 GB, 150 MB/s, 8 MB Cache, 7200 RPM
Managing modules / devices / libraries / etc
% lspci % lsmod % depmod % modprobe # tail /var/log/messages (to check success / failure) % rmmod
% ldd /usr/bin/python # print shared library dependencies linux-gate.so.1 => (0xffffe000) libpython2.5.so.1.0 => /usr/lib/libpython2.5.so.1.0 (0xb7e2e000) libpthread.so.0 => /lib/libpthread.so.0 (0xb7e16000) libdl.so.2 => /lib/libdl.so.2 (0xb7e12000) libutil.so.1 => /lib/libutil.so.1 (0xb7e0e000) libm.so.6 => /lib/libm.so.6 (0xb7de7000) libc.so.6 => /lib/libc.so.6 (0xb7cb9000) /lib/ld-linux.so.2 (0xb7f71000)
Linux networking
see: SuSE wireless card configuration
% /etc/init.d/network restart % route add 20.0.xxx.xxx gateway foo % /etc/rc.local % /etc/sysconfig/network-scripts % /sbin/ifconfig
% netstat -nr Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 20.0.xxx.xx 20.0.xx.xx 255.255.255.0 UGH 0 0 0 eth0
% cat /proc/net/arp IP address HW type Flags HW address Mask Device 192.168.xxx.xxx 0x1 0x2 00:00:00:00:00:00 * eth0 192.168.xxx.xxx 0x1 0x2 00:00:00:00:00:00 * eth0
External resources
- Linux Networking-HOWTO
- Wireless LANs with SuSE Linux
- Quick HOWTO : Ch14 : Linux Firewalls Using iptables
- Ndiswrapper Wiki
- the rt2x00 Open Source Project
Display (Monitor / Graphics Card)
% cat /etc/X11/xorg.conf % xdpyinfo | grep dimen # for screen dimensions
If you are having trouble (in SuSE) getting your monitor to display anything (either from an initial boot or from adding a new monitor), try the following:
- Reboot in Failsafe mode
- Login as root
- At the command prompt type: sax2 -m 0=vesa
- Configure video settings and test them (it is important to test your settings first!)
- Reboot in normal mode.
Backing up the MBR
It is easy to backup and restore the master boot record (MBR) in Linux. However, caution must be exorcised when performing any of the following commands.
- to backup
dd if=/dev/xxx of=mbr.backup bs=512 count=1
- to restore
dd if=mbr.backup of=/dev/xxx bs=512 count=1
where xxx
is the device, which can be hda
, sda
, or any other.
Sound problems
Note, my sound card specs: Intel Corporation 82801EB/ER (ICH5/ICH5R) AC'97 Audio Controller
- Un-mute PCM sound
- Check the following:
% lsmod | grep snd % cat /etc/modprobe.conf % vi /etc/modprobe.d/sound
(change "snd-intel8x0" to "snd_intel8x0")
% ./sbin/lspci
(list sound specs / Multimedia audio controller)
% modprobe snd-via82xx
Hacked?
- Check for failed logins in:
/var/log/messages
- Regularly monitor:
-
zcat /var/log/auth.log.*.gz | grep refused
-
grep -i failed /var/log/auth.log
- last
- w and/or who
- uptime
-
- Verify that
/etc/passwd
hasn't changed. - Check fuser for ports.
- Search for portscans in server report.
- Check for weird processing hogging the CPU.
- Use fail2ban, DenyHosts, etc.
Notes
- pstree — display a tree of processes
- lsmod — program to show the status of modules in the Linux Kernel
- modprobe — program to add and remove modules from the Linux Kernel
- netstat — Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
- lspci — list all PCI devices
- more /usr/share/pci.ids — A list of all known PCI ID's (vendors, devices, classes, and subclasses). Maintained at The Linux PCI ID Repository, use the update-pciids utility to download the most recent version.
External links
- SuSE wiki
- How to get specific programs to run under Dapper Drake 64-bit edition
- the (R)ecovery (I)s (P)ossible Linux rescue system
- Restrict Linux users to their home directories only
- Howto: Formatting Linux Filesystem
- Quick HOWTO : Ch29 : Remote Disk Access with NFS
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