Bash – Debugging hanging bash process

bashtroubleshooting

After some bad performance today, I checked top:

 1  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  14229 myuser    20   0  8776 5264 1684 R   99  0.2   1383:47 bash

98-100% use by a Bash process which should have died a long time ago (I just closed all terminals to verify it)? I'm not sure what's causing it.

$ lsof -p 14229
COMMAND   PID   USER   FD   TYPE DEVICE SIZE/OFF     NODE NAME
bash    14229 myuser  cwd    DIR   0,23     4096 11059271 /home/users/myuser (company.com:/home/users/)
bash    14229 myuser  rtd    DIR    8,2     4096        2 /
bash    14229 myuser  txt    REG    8,2   920788  7617113 /bin/bash
bash    14229 myuser  mem    REG    8,2    30520   657679 /lib/i386-linux-gnu/libnss_compat-2.15.so
bash    14229 myuser  mem    REG    8,2    13940   657672 /lib/i386-linux-gnu/libdl-2.15.so
bash    14229 myuser  mem    REG    8,2  1713640   657666 /lib/i386-linux-gnu/libc-2.15.so
bash    14229 myuser  mem    REG    8,2   121024   660635 /lib/i386-linux-gnu/libtinfo.so.5.9
bash    14229 myuser  mem    REG    8,2    47040   657683 /lib/i386-linux-gnu/libnss_files-2.15.so
bash    14229 myuser  mem    REG    8,2    42652   657690 /lib/i386-linux-gnu/libnss_nis-2.15.so
bash    14229 myuser  mem    REG    8,2   134344   657659 /lib/i386-linux-gnu/ld-2.15.so
bash    14229 myuser  mem    REG    8,2    92016   657678 /lib/i386-linux-gnu/libnsl-2.15.so
bash    14229 myuser  mem    REG    8,2  2919792  7748495 /usr/lib/locale/locale-archive
bash    14229 myuser  mem    REG    8,2    26256  7757442 /usr/lib/i386-linux-gnu/gconv/gconv-modules.cache
bash    14229 myuser    0r   CHR  136,1      0t0        4 /dev/pts/1 (deleted)
bash    14229 myuser    1w   CHR  136,1      0t0        4 /dev/pts/1 (deleted)
bash    14229 myuser    2w   CHR  136,1      0t0        4 /dev/pts/1 (deleted)
bash    14229 myuser  255u   CHR  136,1      0t0        4 /dev/pts/1 (deleted)

Except for the /dev/pts lines this is identical to other bash processes:

COMMAND  PID   USER   FD   TYPE DEVICE SIZE/OFF     NODE NAME
bash    6674 myuser  cwd    DIR   0,23     4096 11059271 /home/users/myuser (company.com:/home/users/)
bash    6674 myuser  rtd    DIR    8,2     4096        2 /
bash    6674 myuser  txt    REG    8,2   920788  7617113 /bin/bash
bash    6674 myuser  mem    REG    8,2  1713640   657666 /lib/i386-linux-gnu/libc-2.15.so
bash    6674 myuser  mem    REG    8,2   121024   660635 /lib/i386-linux-gnu/libtinfo.so.5.9
bash    6674 myuser  mem    REG    8,2    47040   657683 /lib/i386-linux-gnu/libnss_files-2.15.so
bash    6674 myuser  mem    REG    8,2    13940   657672 /lib/i386-linux-gnu/libdl-2.15.so
bash    6674 myuser  mem    REG    8,2    30520   657679 /lib/i386-linux-gnu/libnss_compat-2.15.so
bash    6674 myuser  mem    REG    8,2    42652   657690 /lib/i386-linux-gnu/libnss_nis-2.15.so
bash    6674 myuser  mem    REG    8,2    92016   657678 /lib/i386-linux-gnu/libnsl-2.15.so
bash    6674 myuser  mem    REG    8,2   134344   657659 /lib/i386-linux-gnu/ld-2.15.so
bash    6674 myuser  mem    REG    8,2  2919792  7748495 /usr/lib/locale/locale-archive
bash    6674 myuser  mem    REG    8,2    26256  7757442 /usr/lib/i386-linux-gnu/gconv/gconv-modules.cache
bash    6674 myuser    0r   CHR  136,2      0t0        5 /dev/pts/2
bash    6674 myuser    1w   CHR  136,2      0t0        5 /dev/pts/2
bash    6674 myuser    2w   CHR  136,2      0t0        5 /dev/pts/2
bash    6674 myuser  255u   CHR  136,2      0t0        5 /dev/pts/2

Standard kill doesn't work:

$ kill 14229 && sleep 1m && kill -0 14229 && echo Alive
Alive

According to ps wafux it has no child processes.

Tried tracing it as recommended by @ChandraRavoori:

$ sudo strace -p 14229
Process 14229 attached - interrupt to quit

After that I get no output. I tried to kill 14229 multiple times, and it just printed the following every time:

--- SIGTERM (Terminated) @ 0 (0) ---

What are other things to check before kill -9?

Best Answer

Try

strace -p 14229

I will print every syscall that the process invokes. Then you see what the process actually does.

http://try-linux.blogspot.de/2013/12/how-to-strace-process.html

Related Solutions

Linux network troubleshooting and debugging

I think, general principles of network troubleshooting are:

Find out at what level of TCP/IP stack(or some other stack) occurs the problem.
Understand what is the correct system behavior, and what is deviation from normal system state
Try to express the problem in one sentence or in several words
Using obtained information from buggy system, your own experience and experience of other people(google, various forum, etc.), try to solve the problem until success(or failure)
If you fail, ask other people about help or some advice

As for me, I usually obtain all required information using all needed tools, and try to match this information to my experience. Deciding what level of network stack contains the bug helps to cut off unlikely variants. Using experience of other people helps to solve the problems quickly, but often it leads to situation, that I can solve some problem without its understanding and if this problem occurs again, it's impossible for me to tackle it again without the Internet.

And in general, I don't know how I solve network problems. It seems that there is some magic function in my brain named SolveNetworkProblem(information_about_system_state, my_experience, people_experience), which could sometimes return exactly the right answer, and also could sometimes fail(like here TCP dies on a Linux laptop).

I usually use utils from this set for network debugging:

ifconfig (or ip link, ip addr) - for obtaining information about network interfaces
ping - for validating, if target host is accessible from my machine. ping is also could be used for basic DNS diagnostics - we could ping host by IP-address or by its hostname and then decide if DNS works at all. And then traceroute or tracepath or mtr to look what's going on on the way there.
dig - diagnose everything DNS
dmesg | less or dmesg | tail or dmesg | grep -i error - for understanding what the Linux kernel thinks about some trouble.
netstat -antp + | grep smth - my most popular usage of netstat command, which shows information about TCP connections. Often I perform some filtering using grep. See also the new ss command (from iproute2 the new standard suite of Linux networking tools) and lsof as in lsof -ai tcp -c some-cmd.
telnet <host> <port> - is very useful for communicating with various TCP-services(e.g. on SMTP, HTTP protocols), also we could check general opportunity to connect to some TCP port.
iptables-save (on Linux) - to dump the full iptables tables
ethtool - get all the network interface card parameters (status of the link, speed, offload parameters...)
socat - the swiss army tool to test all network protocols (UDP, multicast, SCTP...). Especially useful (more so than telnet) with a few -d options.
iperf - to test bandwidth availability
openssl (s_client, ocsp, x509...) to debug all SSL/TLS/PKI issues.
wireshark - the powerful tool for capturing and analyzing network traffic, which allows you to analyze and catch many network bugs.
iftop - show big users on the network/router.
iptstate (on Linux) - current view of the firewall's connection tracking.
arp (or the new (Linux) ip neigh) - show the ARP-table status.
route or the newer (on Linux) ip route - show the routing table status.
strace (or truss, dtrace or tusc depending on the system) - is useful tool which shows what system calls does the problem process, it also shows error codes(errno) when system calls fails. This information often says enough for understanding the system behavior and solving a problem. Alternatively, using breakpoints on some networking functions in gdb can let you find out when they are made and with which arguments.
to investigate firewall issues on Linux: iptables -nvL shows how many packets are matched by each rule (iptables -Z to zero the counters). The LOG target inserted in the firewall chains is useful to see which packets reach them and how they have already been transformed when they get there. To get further NFLOG (associated with ulogd) will log the full packet.

Bash – See the expansion of Bash variables for debugging

Run the script under bash -x:

$ bash -x script
+ DIR=/var/tmp
+ FILE=/var/tmp/file
+ SCRIPT_ROOT=/opt/root
+ TOOL=/opt/root/tool.sh
+ /opt/root/tool.sh /var/tmp/file

While -x is normally used for debugging, it seems to meet your needs.

Documentation

From man bash:

-x Print commands and their arguments as they are executed.

Best Answer

Related Solutions

Linux network troubleshooting and debugging

Bash – See the expansion of Bash variables for debugging

Documentation

Related Question