Embedded Files
APIs
APIs
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
rt_sigaction(SIGCHLD, {SIG_DFL, [], SA_RESTORER|SA_RESTART, 0x7f101522e4a0},{SIG_DFL, [], 0}, 8) = 0
brk(0x1cab000) = 0x1cab000
mprotect(0x7f1014ff8000, 2093056, PROT_NONE) = 0
fstat(3, {st_mode=S_IFREG|0644, st_size=93128, ...}) = 0
wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 363
stat("/usr/local/sbin/rm", 0x7ffc88cc3710) = -1 ENOENT (No such file or directory)
Command
Command
cut command
To get substring from each line (for example first three characters)
Useful link:https://www.geeksforgeeks.org/cut-command-linux-examples/
To know disk space allocated for current directory
To know disk space allocated for current directory
df -h . -> gives available disk space in current directory
Example:
root@fa6a6992af99:/var# df -h .
Filesystem Size Used Avail Use% Mounted on
none 93G 80G 8.5G 91% /
root@fa6a6992af99:/var# cd /dev/
df -TH . -> gives file system type info
Example:
root@4f7668179169:/# cd /var/
root@4f7668179169:/var# df -TH .
Filesystem Type Size Used Avail Use% Mounted on
none aufs 100G 69G 26G 74%
To know how many vCPUs are present in the machine
To know how many vCPUs are present in the machine
You can see the usage of your CPU cores using top command.
Open a Terminal.
Type top. You will see some information about tasks, memory etc.
Type 1 to show individual CPU usage. You will see something like:
View process is pinned to which vCPU
View process is pinned to which vCPU
[root@ubuntu ~]# taskset -p 1
pid 1's current affinity mask: 3f
To display stack trace in running process
To display stack trace in running process
__builtin_return_address(X) --> This API will get the stack frame address of frame X
How to create daemon process
How to create daemon process
daemon -> This API detaches current process from the associated terminal and rather, make a background process running as daemon
Calling cleanup function in case normal exit of process
Calling cleanup function in case normal exit of process
A process normal terminatation can be caused by exit() API call or main function return. atexit() function defines custom API which is called whenever normal termination. In case of abnormal termination(signals, abort()), it is not invoked.
likely/unlikely macro for code level optimization
likely/unlikely macro for code level optimization
http://stackoverflow.com/questions/109710/likely-unlikely-macros-in-the-linux-kernel-how-do-they-work-whats-their describes about this. It allows programmer to mention which result is likely. This is used for optimizing code.
Remove debug symbol from an executable
Remove debug symbol from an executable
The GNU objcopy utility copies the contents of an object file to another.
objcopy --strip-debug hello_world.debug hello_world --> strip off debug symbol from hello_world.debug and output stripped hello_world
Create archive (static library) file
Create archive (static library) file
ar rcsuv test.a $(OBJS) --> creates archive
ranlib test.a ---> createindex for the archive which helps to speedup liniking of library
Makefile example for archive
CC=gcc
CFLAGS=-I.
SRCS= hellomake.c \
hellofunc.c
DEPS=hellomake.h
OUT=hellomake
.c.o: $(DEPS)
$(CC) -c $< $(CFLAGS) -o $@
OBJS:=$(SRCS:.c=.o)
all:myar hellomake
myar: $(OBJS)
ar rcsuv test.a $(OBJS)
ranlib test.a
hellomake::$(OBJS)
$(CC) -o $(OUT) $(OBJS) $(CFLAGS1)
clean:
rm -rf *.o
rm -rf $(OUT)
---------------------------
[root@ubuntu /personal/testcode/makefile_learning]# make myar
gcc -c hellomake.c -I. -o hellomake.o
gcc -c hellofunc.c -I. -o hellofunc.o
ar rcsuv test.a hellomake.o hellofunc.o
r - hellomake.o
r - hellofunc.o
ranlib test.a
Ignore hidden files in find command
Ignore hidden files in find command
find src/ -not -path '*/\.*' -type f
Remount a device
Remount a device
sudo mount -o remount,rw /partition/identifier /mount/point
Ccache for faster compilation
Ccache for faster compilation
ccache is a compiler cache. It speeds up recompilation by caching the result of previous compilations and detecting when the same compilation is being done again. Supported languages are C, C++, Objective-C and Objective-C++.
Configure network namespace
Configure network namespace
A network namespace is logically another copy of the network stack, with its own routes, firewall rules, and network devices. It can be managed using "ip netns" command as shown below.
ip netns delete mynamespace --> remove namespace
ip netns add mynamespace -> add namespace
Create virtual interfaces and link between two interfaces
Create virtual interfaces and link between two interfaces
Use ip link add command
ip link add command to create virtual interfaces test and testp
[root@ubuntu /personal/techfair]# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
link/ether 72:73:1c:31:86:61 brd ff:ff:ff:ff:ff:ff
3: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default
link/ether 02:42:52:5a:80:f8 brd ff:ff:ff:ff:ff:ff
5: veth5c04037: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP mode DEFAULT group default
link/ether 9a:8f:24:86:41:a8 brd ff:ff:ff:ff:ff:ff
2054: br-96900f6adc12: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
link/ether 02:42:e2:73:0c:8c brd ff:ff:ff:ff:ff:ff
2071: br-b10c04cf75eb: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
link/ether 02:42:cc:72:10:11 brd ff:ff:ff:ff:ff:ff
2173: vethcpx0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether be:c9:86:d6:5a:2f brd ff:ff:ff:ff:ff:ff
[root@ubuntu /personal/techfair]# ip link add test type veth peer name testp
[root@ubuntu /personal/techfair]# ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
link/ether 72:73:1c:31:86:61 brd ff:ff:ff:ff:ff:ff
3: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default
link/ether 02:42:52:5a:80:f8 brd ff:ff:ff:ff:ff:ff
5: veth5c04037: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP mode DEFAULT group default
link/ether 9a:8f:24:86:41:a8 brd ff:ff:ff:ff:ff:ff
2054: br-96900f6adc12: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
link/ether 02:42:e2:73:0c:8c brd ff:ff:ff:ff:ff:ff
2071: br-b10c04cf75eb: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
link/ether 02:42:cc:72:10:11 brd ff:ff:ff:ff:ff:ff
2173: vethcpx0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether be:c9:86:d6:5a:2f brd ff:ff:ff:ff:ff:ff
2178: testp: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 1a:15:a5:69:02:7d brd ff:ff:ff:ff:ff:ff
2179: test: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 2e:64:dd:0c:0d:0c brd ff:ff:ff:ff:ff:ff
Add link between virtual interfaces
ip link manages virtual link
ip link set - change device attributes
ip link delete - delete virtual link
ip link add - add virtual link
ip link show -> shows the interface if up
ip addr del $DOCKERIP dev eth0 --> remove IP from eth0
ip link set eth0 down -> set eth0 down
ip link set eth0 name ns0 -> rename eth0 to ns0
ip link set ns0 up -> ns0 up
ip link add ns1 mtu $MTU type veth peer name ns2 mtu $MTU -> Add link between ns1 and ns2
ip addr add $LOOPIP/$DOCKER_MASK dev ns2 -> Create ns2 virtual interface
ip link set ns1 up -> ns1 up
ip link set ns2 up -> ns2 up
ip route add default via $SNIP -> add default route
ip link set eth10 netns myns -> move interface from host namespace to myns namespace
ip netns exec mynsip link set eth10 netns 1 -> move interface from myns namespace to host namespace
Useful link: http://linux-ip.net/html/tools-ip-link.html#tools-ip-link-set-name
https://serverfault.com/questions/704700/how-can-i-move-an-interface-out-of-a-network-namespace
Useful command to play with interface ip address
Useful command to play with interface ip address
ip addr show eth0-> shows ip addr of interface
ip addr add 172.25.0.15/16 dev eth1 -> adds an IP to the interface eth1
ip addr del 172.25.0.15/16 dev eth1 -> removes an IP from the interface eth1
Method to automate ssh login with password
Method to automate ssh login with password
Use either of sshpass command, expect shell or python script
expect shell and python script will be better since it will work well with ssh alone in remote machine, however sshpass should be installed in remote machine as well.
Useful link: https://serverfault.com/questions/241588/how-to-automate-ssh-login-with-password
https://stackoverflow.com/questions/43526330/shell-script-to-automate-ssh-login-using-password
Method to calculate elapsed time in Linux at nanoseconds granularity
Method to calculate elapsed time in Linux at nanoseconds granularity
Example to calculate time difference
#include <time.h>
#include <stdlib.h>
struct timespec g_dk_starttime;
struct timespec g_dk_endtime;
int g_dk_diff_sec = 0;
int g_dk_diff_nsec = 0;
int ns_stub_gettimeelapsed(int reset, int *secs, int *nsecs)
{
if(reset) {
if (clock_gettime(CLOCK_MONOTONIC, &g_dk_starttime ) == -1) {
abort();
}
return 0;
}
else{
if (clock_gettime(CLOCK_MONOTONIC, &g_dk_endtime ) == -1) {
abort();
}
g_dk_diff_sec = g_dk_endtime.tv_sec - g_dk_starttime.tv_sec;
g_dk_diff_nsec = g_dk_endtime.tv_nsec - g_dk_starttime.tv_nsec;
if(g_dk_diff_nsec<0) {
--g_dk_diff_sec;
g_dk_diff_nsec += 1000000000;
}
g_dk_starttime = g_dk_endtime;
*secs = g_dk_diff_sec;
*nsecs = g_dk_diff_nsec;
return g_dk_diff_sec;
}
}
Useful link: https://linux.die.net/man/3/clock_gettime
https://gist.github.com/pfigue/9ce8a2c0b14a2542acd7
To find CPU architecture of archive file (.a file)
To find CPU architecture of archive file (.a file)
Example to find CPU architecture of archive file (.a file)
root# readelf -h libevent-2.0.22-stable/.libs/libevent.a | grep 'Class\|File\|Machine' | more
File: libevent-2.0.22-stable/.libs/libevent.a(event.o)
Class: ELF64
Machine: Advanced Micro Devices X86-64
File: libevent-2.0.22-stable/.libs/libevent.a(evthread.o)
Class: ELF64
Machine: Advanced Micro Devices X86-64
File: libevent-2.0.22-stable/.libs/libevent.a(buffer.o)
Here the .a file has 64 bit architecutre (X86-64)
Changing maximum possible shared memory size
Changing maximum possible shared memory size
/proc/sys/kernel/shmmax maintains this info
echo 200000 >/proc/sys/kernel/shmmax
Method to recovery of a faulty hard-drive
Method to recovery of a faulty hard-drive
fsck is used to check and optionally repair one or more Linux file systems.
Refer:https://linux.die.net/man/8/fsck
Method to clone a hard disk
Method to clone a hard disk
Disk cloning is the process of copying the contents of one computer hard disk to another disk or to an "image" file.
Linux dd command can be used for the same.
Refer: https://wiki.archlinux.org/index.php/disk_cloning
Method to provide custom search path for libraries in programmatic manner
Method to provide custom search path for libraries in programmatic manner
Linux ldconfig uses /etc/ld.so.conf to load default library path. By default, it will use /etc/ld.so.conf.d/*.conf for the same. So, simply add a custom path in this directory
Refer: http://www.tutorialspoint.com/unix_commands/ldconfig.htm
How to know start time of a process
ps -eo pid,cmd,lstart | grep <process name/PID>
Refer http://stackoverflow.com/questions/5731234/how-to-get-the-start-time-of-a-long-running-linux-process
Method to know CPU number of cores
Method to know CPU number of cores
[root@ubuntu /personal/testcode/makefile_learning]# getconf _NPROCESSORS_ONLN
8
[root@ubuntu /personal/testcode/makefile_learning]# nproc --all 8
Useful link: http://stackoverflow.com/questions/6481005/how-to-obtain-the-number-of-cpus-cores-in-linux-from-the-command-line
How to see bridge networks in Linux
How to see bridge networks in Linux
brctl show
Refer: https://docs.docker.com/engine/userguide/networking/default_network/custom-docker0/
Method to configure path to dump core
Method to configure path to dump core
kernel.core_pattern sysctl parameter is used for this.
sysctl -w kernel.core_pattern=/var/crash/core.%e.%p
Linux kernel will generate file /proc/sys/kernel/core_pattern
root@222db56babfa:/# cat /proc/sys/kernel/core_pattern
/var/crash/core.%e.%p
root@222db56babfa:/# ls /var/crash core.myproc.132 core.myproc.324 core.myproc.128
Method to know environment variable for a running process
Method to know environment variable for a running process
use /proc/<pid>/environ data
Getting environment variable detail for running process
root@ubuntu:/# ps -aef
UID PID PPID C STIME TTY TIME CMD
root 1 0 0 Jan01 ? 00:00:00 /bin/sh -c bash -C '/var/netscaler/bins/docker_startup.sh'
root 6 1 0 Jan01 ? 00:00:00 bash -C /var/netscaler/bins/docker_startup.sh
root 49 1 0 Jan01 ? 00:00:00 /usr/sbin/sshd
root 50 1 1 Jan01 ? 00:12:26 /var/netscaler/bins/nsppe 1
root 54 1 0 Jan01 ? 00:10:48 /var/netscaler/bins/nslinuxtimer
root 55 1 0 Jan01 ? 00:00:01 /var/netscaler/contrib/httpd/bin/httpd -k start -f /var/netscaler/contrib/httpd/conf/httpd.conf
daemon 56 55 0 Jan01 ? 00:00:00 /var/netscaler/contrib/httpd/bin/httpd -k start -f /var/netscaler/contrib/httpd/conf/httpd.conf
daemon 57 55 0 Jan01 ? 00:00:00 /var/netscaler/contrib/httpd/bin/httpd -k start -f /var/netscaler/contrib/httpd/conf/httpd.conf
daemon 58 55 0 Jan01 ? 00:00:00 /var/netscaler/contrib/httpd/bin/httpd -k start -f /var/netscaler/contrib/httpd/conf/httpd.conf
daemon 59 55 0 Jan01 ? 00:00:00 /var/netscaler/contrib/httpd/bin/httpd -k start -f /var/netscaler/contrib/httpd/conf/httpd.conf
daemon 60 55 0 Jan01 ? 00:00:00 /var/netscaler/contrib/httpd/bin/httpd -k start -f /var/netscaler/contrib/httpd/conf/httpd.conf
root 65 1 0 Jan01 ? 00:00:43 /var/netscaler/bins/nsaggregatord -i 192.0.0.2
root 70 65 0 Jan01 ? 00:00:00 [nsaggregatord] <defunct>
root 81 1 0 Jan01 ? 00:00:02 /var/netscaler/bins/snmpd
root 89 1 0 Jan01 ? 00:00:02 /var/netscaler/bins/nslped
root 96 1 0 Jan01 ? 00:00:02 /var/netscaler/bins/nsnetsvc -S
root 103 1 0 Jan01 ? 00:00:03 /var/netscaler/bins/nsconfigd -S
root 110 1 0 Jan01 ? 00:00:01 /var/netscaler/bins/nstraceaggregator
root 187 6 0 Jan01 ? 00:01:23 monit -I
root 188 0 0 Jan01 ? 00:00:00 bash
daemon 248 55 0 Jan01 ? 00:00:00 /var/netscaler/contrib/httpd/bin/httpd -k start -f /var/netscaler/contrib/httpd/conf/httpd.conf
root 302 0 0 Jan01 ? 00:00:00 bash
root 622 302 0 04:38 ? 00:00:00 vi nstriton.py
root 623 188 0 04:42 ? 00:00:00 python -m pdb /var/netscaler/triton/nstriton.py --kube-apiserver https://10.102.53.236:6443 --logfilename /var/log/nstriton.log
root 667 0 0 05:10 ? 00:00:00 bash
root 684 667 0 05:14 ? 00:00:00 ps -aef
root@ubuntu:/# cat /proc/623/environ
NS_NETMODE=HOSTNS_TYPE=CPXNS_USER=nsrootNS_IP_RANGE=NS_PASSWORD=nsrootNS_MGMT_SERVER=NS_IP=192.168.1.2LS_PORT=27000HOSTNAME=ubuntuCPX_CORES=1TERM=xtermLS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:BANDWIDTH=1000PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/var/netscaler/binsCPX_MAX_MEM=1024PWD=/SHLVL=1HOME=/rootNOTVISIBLE=in users profileLESSOPEN=| /usr/bin/lesspipe %sEULA=yesLESSCLOSE=/usr/bin/lesspipe %s %s_=/usr/bin/pythonroot@ubuntu:/#
Useful link: https://serverfault.com/questions/66363/environment-variables-of-a-running-process-on-unix
Method to change notification limit for the number of file descriptors
Method to change notification limit for the number of file descriptors
Use sysctl with fs.inotify.max_user_instances
[root@ubuntu ~]# sysctl fs.inotify.max_user_instances
fs.inotify.max_user_instances = 128
[root@ubuntu ~]# sysctl -w fs.inotify.max_user_instances=1024
tail -f /var/log/dmesg will have log if number is reached the limit
Useful link: https://unix.stackexchange.com/questions/13751/kernel-inotify-watch-limit-reached
Method to know MTU of an interface in Linux
Method to know MTU of an interface in Linux
netstat -i will help
netstat command to see MTU
root@server1:~# netstat -i
Kernel Interface table
Iface MTU RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg
docker0 1500 0 0 0 0 0 0 0 0 BMU
eth0 1200 155644002 0 0 0 42812749 0 0 0 BMRU
lo 65536 3954341 0 0 0 3954341 0 0 0 LRU
Useful link:-http://stackoverflow.com/questions/29236554/how-can-i-determine-the-mtu-value-on-linux
Method to disable assembly of tcp segments at the linux driver level for an interface
Method to disable assembly of tcp segments at the linux driver level for an interface
ethtool will help for this.
ethtool will control docker bridge interface
>> To disable assembly of tcp segments
root@ubuntu:~/personal# ethtool -K docker0 tx off rx off tso off
Cannot change rx-checksumming
Actual changes:
tx-checksumming: off
tx-checksum-ip-generic: off
tcp-segmentation-offload: off
tx-tcp-segmentation: off
tx-tcp-ecn-segmentation: off
tx-tcp6-segmentation: off
udp-fragmentation-offload: off [requested on]
>> To enable assembly of tcp segments
root@ubuntu:~/personal# ethtool -K docker0 tx on rx on tso on
Cannot change rx-checksumming
Actual changes:
tx-checksumming: on
tx-checksum-ip-generic: on
tcp-segmentation-offload: on
tx-tcp-segmentation: on
tx-tcp-ecn-segmentation: on
tx-tcp6-segmentation: on
udp-fragmentation-offload: on
Useful link - https://en.wikipedia.org/wiki/Large_receive_offload
Method to convert new line into space
Method to convert new line into space
tr command will be useful
ls -l | awk '{print $9}' | tr '\n' ' '
Useful link:-http://stackoverflow.com/questions/1251999/how-can-i-replace-a-newline-n-using-sed
How to list folder usage for in subfolders only without going any depth further
How to list folder usage for in subfolders only without going any depth further
--max-depth=1 option will help in this regard
[root@ubuntu /]# du -h --max-depth=1 /var/
4.0K /var/opt
4.0K /var/www
184M /var/cache
1.3M /var/spool
18M /var/log
32K /var/mail
4.0K /var/tmp
9.4M /var/backups
Useful link: https://www.peterbe.com/plog/du-max-depth
Method to know the standard header file location in g++/gcc
Method to know the standard header file location in g++/gcc
Capture output with pre-processing(Refer -E compiler option). Then open the file and look at the path from which header file is added.
Text Box
test2.cpp:
#include <array>
using namespace std;
int main(void) {
}
[root@ubuntu /personal/multi_intf_aut]# g++ -std=c++11 -E -o test2.e test2.cpp
Now test2.e will have include file path as below
# 1 "/usr/include/c++/4.8/array" 1 3
Method to print segment of lines in the log file (from line X to line Y)
Method to print segment of lines in the log file (from line X to line Y)
Use combination of tail and head commands
Display segment of file content
X=2
Y=10
< infile.txt head -n "$Y" | tail -n +"$X"
Below example provides the way to display lines 2 to 10 in file infile.txt
[root@ubuntu /personal/multi_intf_aut]# X=2
[root@ubuntu /personal/multi_intf_aut]# Y=10
[root@ubuntu /personal/multi_intf_aut]# < infile.txt head -n "$Y" | tail -n +"$X"
import subprocess
import json
import re
import time
import urllib2
import urllib
import base64
import copy
import argparse
[root@ubuntu /personal/multi_intf_aut]# head -n 10 infile.txt
#!/usr/bin/env python
import subprocess
import json
import re
import time
import urllib2
import urllib
import base64
import copy
import argparse
Useful link:https://unix.stackexchange.com/questions/47407/cat-line-x-to-line-y-on-a-huge-file
Method to read file when connected via SSH
Method to read file when connected via SSH
Display output to console (using cat/tail). It will be returned as console result to SSH command.
Method to yield CPU using epoll
Method to yield CPU using epoll
Below example will yield CPU for 1 milliseconds
epoll_wait (ep_fd, events, maxevents , 1);
useful link: http://man7.org/linux/man-pages/man2/epoll_wait.2.html
Method to ignore fd in epoll_wait in case fd is not read
Use EPOLLET while setting fd.
Example of using EPOLLET
#include <iostream>
#include <cerrno>
#include <cstring>
#include <cstdlib>
#include <sys/fcntl.h>
#include <unistd.h>
// EPOLL & TIMER
#include <sys/epoll.h>
#include <sys/timerfd.h>
int main(int argc, char **argv)
{
/* epoll instance */
int efd = epoll_create1(EPOLL_CLOEXEC);
if (efd < 0)
{
std::cerr << "epoll_create error: " << strerror(errno) << std::endl;
return EXIT_FAILURE;
}
struct epoll_event ev;
struct epoll_event events[128];
/* timer instance */
int tfd = timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC);
struct timespec ts;
// first expiration in 3. seconds after program start
ts.tv_sec = 3;
ts.tv_nsec = 0;
struct itimerspec new_timeout;
struct itimerspec old_timeout;
bzero(&new_timeout, sizeof(new_timeout));
bzero(&old_timeout, sizeof(old_timeout));
// value
new_timeout.it_value = ts;
// no interval;
// timer will be armed in epoll_wait event trigger
new_timeout.it_interval.tv_sec =
new_timeout.it_interval.tv_nsec = 0;
// Add the timer descriptor to epoll.
if (tfd != -1)
{
ev.events = EPOLLIN | EPOLLET;
ev.data.ptr = &tfd;
epoll_ctl(efd, EPOLL_CTL_ADD, tfd, &ev);
}
int flags = 0;
if (timerfd_settime(tfd, flags, &new_timeout, &old_timeout) < 0)
{
std::cerr << "timerfd_settime error: " << strerror(errno) << std::endl;
}
int numEvents = 0;
int timeout = 0;
bool checkTimer = false;
while (1)
{
checkTimer = false;
numEvents = epoll_wait(efd, events, 128, timeout);
if (numEvents > 0)
{
for (int i = 0; i < numEvents; ++i)
{
if (events[i].data.ptr == &tfd)
{
std::cout << "timeout" << std::endl;
checkTimer = true;
}
}
}
else if(numEvents == 0)
{
continue;
}
else
{
std::cerr << "An error occured: " << strerror(errno) << std::endl;
}
if (checkTimer)
{
/* Check data storage */
uint64_t value;
ssize_t readBytes;
//while ( (readBytes = read(tfd, &value, 8)) > 0)
//{
// std::cout << "\tread: '" << value << "'" << std::endl;
//}
itimerspec new_timeout;
itimerspec old_timeout;
new_timeout.it_value.tv_sec = rand() % 3 + 1;
new_timeout.it_value.tv_nsec = 0;
new_timeout.it_interval.tv_sec =
new_timeout.it_interval.tv_nsec = 0;
timerfd_settime(tfd, flags, &new_timeout, &old_timeout);
}
}
return EXIT_SUCCESS;
}
Useful link:https://stackoverflow.com/questions/12102740/epoll-with-timerfd
https://stackoverflow.com/questions/12491629/timerfd-and-read
Method to configure timerfd with epoll
Sample code to set timerfd with epoll
#include <stdio.h>
#include <errno.h>
#include <sys/timerfd.h>
#include <sys/epoll.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#define IDLE_TIMERFD_UNINTIALIZED (-1)
static int g_timerfd_for_idle_timeout = IDLE_TIMERFD_UNINTIALIZED;
struct epoll_event ev;
static int timer_set_idle_wait_timeout(int epfd)
{
struct itimerspec timerSpec;
int result = -1;
/*create timer fd*/
if(g_timerfd_for_idle_timeout != IDLE_TIMERFD_UNINTIALIZED){
//Already initialized
return 0;
}
g_timerfd_for_idle_timeout = timerfd_create(CLOCK_MONOTONIC, 0);
if (g_timerfd_for_idle_timeout == IDLE_TIMERFD_UNINTIALIZED) {
goto ERR;
}
/*Set time frequency*/
memset(&timerSpec, 0, sizeof(timerSpec));
timerSpec.it_value.tv_sec = 0;
timerSpec.it_value.tv_nsec = 900000;//0.9 millisecond
timerSpec.it_interval.tv_sec = 0;
timerSpec.it_interval.tv_nsec = 900000;//0.9 millisecond
result = timerfd_settime(g_timerfd_for_idle_timeout, 0, &timerSpec, NULL);
if (result == -1) {
goto ERR;
}
/* Register timer fd with epoll*/
ev.events = EPOLLIN | EPOLLET;
ev.data.ptr = NULL;
result = epoll_ctl(epfd, EPOLL_CTL_ADD, g_timerfd_for_idle_timeout, &ev);
if (result == -1) {
goto ERR;
}
return 0;
ERR:
if(g_timerfd_for_idle_timeout != IDLE_TIMERFD_UNINTIALIZED){
close(g_timerfd_for_idle_timeout);
g_timerfd_for_idle_timeout = IDLE_TIMERFD_UNINTIALIZED;
}
return -1;
}
int main()
{
int result = 0;
uint64_t exp;
int epfd = epoll_create(1);
if (epfd == -1) {
printf("epoll_create() failed: errno=%d\n", errno);
return -1;
}
if(g_timerfd_for_idle_timeout == IDLE_TIMERFD_UNINTIALIZED) {
/*Initialize idle wait timeout*/
result = timer_set_idle_wait_timeout(epfd);
if (result != 0) {
abort();
}
}
int nfds = epoll_wait (epfd, &ev, 10, 1);
//read timer data
int size = read(g_timerfd_for_idle_timeout, &exp, sizeof(uint64_t));
printf("%ld\n", exp);
return 0;
}
========
Output:
root@5b02a27866d0:~# ./a.out
1
Useful link: https://stackoverflow.com/questions/12491629/timerfd-and-read
Method to remove common suffix from filenames in a directory
Method to remove common suffix from filenames in a directory
remove suffix .sample from each files in a directory
root@ubuntu:/etc/quagga# for file in `ls | xargs -0 | grep sample`; do echo $file | grep sample;done
babeld.conf.sample
bgpd.conf.sample
isisd.conf.sample
ospf6d.conf.sample
ospfd.conf.sample
pimd.conf.sample
ripd.conf.sample
ripngd.conf.sample
vtysh.conf.sample
zebra.conf.sample
root@ubuntu:/etc/quagga# for file in `ls | xargs -0 | grep sample`; do mv $file `echo $file | sed 's/.sample//'` ;done
remoll
total 56
drwxrwxr-x 2 quagga quaggavty 4096 Oct 31 02:10 ./
drwxr-xr-x 92 root root 4096 Oct 31 01:53 ../
-rw-r--r-- 1 root root 655 Oct 31 01:56 babeld.conf
-rw-r--r-- 1 root root 582 Oct 31 01:56 bgpd.conf
-rw-r----- 1 quagga quagga 992 Oct 26 02:04 daemons
-rw-r----- 1 quagga quaggavty 945 Oct 18 2016 debian.conf
-rw-r--r-- 1 root root 805 Oct 31 01:56 isisd.conf
-rw-r--r-- 1 root root 1110 Oct 31 01:56 ospf6d.conf
-rw-r--r-- 1 root root 182 Oct 31 01:56 ospfd.conf
-rw-r--r-- 1 root root 992 Oct 31 01:56 pimd.conf
-rw-r--r-- 1 root root 422 Oct 31 01:56 ripd.conf
-rw-r--r-- 1 root root 390 Oct 31 01:56 ripngd.conf
-rw-r--r-- 1 root root 126 Oct 31 01:56 vtysh.conf
-rw-r--r-- 1 root root 385 Oct 31 01:56 zebra.conf
Useful link: https://stackoverflow.com/questions/9984748/how-do-i-get-sed-to-read-from-standard-input
Method to add an existing user as sudoer
Method to add an existing user as sudoer
Use below command
sudo usermod -a -G sudo <username>
useful link: https://askubuntu.com/questions/168280/how-do-i-grant-sudo-privileges-to-an-existing-user
useful link: https://askubuntu.com/questions/168280/how-do-i-grant-sudo-privileges-to-an-existing-user
Method to perform HTTP Post request using curl (curl http post )
Method to perform HTTP Post request using curl (curl http post )
Use curl -X POST
Perform HTTP Post message
root@master:~# curl -v -H "Content-Type: application/json" -X POST -d '{ "login":{"username": "nsroot", "password": "nsroot", "tim
eout": 600}}'
http://192.168.1.2:80/nitro/v1/config/login
Note: Unnecessary use of -X or --request, POST is already inferred.
* Trying 192.168.1.2...
* Connected to 192.168.1.2 (192.168.1.2) port 80 (#0)
> POST /nitro/v1/config/login HTTP/1.1
> Host: 192.168.1.2
> User-Agent: curl/7.47.0
> Accept: */*
> Content-Type: application/json
> Content-Length: 71
>
* upload completely sent off: 71 out of 71 bytes
< HTTP/1.1 201 Created
< Date: Tue, 13 Feb 2018 05:46:47 GMT
< Server: Apache/2.2.32 (Unix) PHP/7.0.13
< X-Powered-By: PHP/7.0.13
< Set-Cookie: PHPSESSID=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; Max-Age=0; path=/
< Expires: Thu, 19 Nov 1981 08:52:00 GMT
< Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
< Pragma: no-cache
< Set-Cookie: sessionid=%23%23E50D453C94B32D09D2464267749DB14603902CF251879EAE2F8A4C552499053A65571E9DC5A773F460BDA14325B981215EA5A3628D39AAEDEDA4204B59223CAD62408AD60EAACA25C960D0CFD04ED15CD24AC1C28E97E6F432AE23197E97BAF3FF5253A157772D7128D4615395A8566537E95212CFAC2331582C5D5F844A; path=/nitro/v1
< Content-Length: 328
< Content-Type: application/json; charset=utf-8
<
* Connection #0 to host 192.168.1.2 left intact
{ "errorcode": 0, "message": "Done", "severity": "NONE", "sessionid": "##E50D453C94B32D09D2464267749DB14603902CF251879EAE2F8A4C552499053A65571E9DC5A773F460BDA14325B981215EA5A3628D39AAEDEDA4204B59223CAD62408AD60EAACA25C960D0CFD04ED15CD24AC1C28E97E6F432AE23197E97BAF3FF5253A157
root@master:~#
Useful link: https://stackoverflow.com/questions/7172784/how-to-post-json-data-with-curl-from-terminal-commandline-to-test-spring-rest
Method to perform HTTP HEAD request using curl (curl http post )
Method to perform HTTP HEAD request using curl (curl http post )
Use 'curl -X HEAD'
Getting HEADER data
$ curl -X HEAD -v -k http://10.102.53.235
Warning: Setting custom HTTP method to HEAD with -X/--request may not work the
Warning: way you want. Consider using -I/--head instead.
* Rebuilt URL to: http://10.102.53.235/
* Trying 10.102.53.235...
* TCP_NODELAY set
* Connected to 10.102.53.235 (10.102.53.235) port 80 (#0)
> HEAD / HTTP/1.1
> Host: 10.102.53.235
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Date: Wed, 28 Mar 2018 10:15:35 GMT
< Server: Apache
< X-Frame-Options: DENY
< Content-Type: text/html; charset=UTF-8
* no chunk, no close, no size. Assume close to signal end
<
Useful link:https://serverfault.com/questions/140149/difference-between-curl-i-and-curl-x-head
Method for curl command to enable redirect link - 302
Method for curl command to enable redirect link - 302
Use -L option
curl redirect follow
[root@ubuntu /personal/sanityissue/cpx]# curl -v google.com
* Rebuilt URL to: google.com/
* Hostname was NOT found in DNS cache
* Trying 216.58.197.78...
* Connected to google.com (216.58.197.78) port 80 (#0)
> GET / HTTP/1.1
> User-Agent: curl/7.35.0
> Host: google.com
> Accept: */*
>
< HTTP/1.1 302 Found
< Cache-Control: private
< Content-Type: text/html; charset=UTF-8
< Referrer-Policy: no-referrer
< Location: http://www.google.co.in/?gfe_rd=cr&dcr=0&ei=t3QwWrPiNcKL8QfVhaZQ
< Content-Length: 269
< Date: Wed, 13 Dec 2017 00:30:47 GMT
<
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>302 Moved</TITLE></HEAD><BODY>
<H1>302 Moved</H1>
The document has moved
<A HREF="http://www.google.co.in/?gfe_rd=cr&dcr=0&ei=t3QwWrPiNcKL8QfVhaZQ">here</A>.
</BODY></HTML>
* Connection #0 to host google.com left intact
[root@ubuntu /personal/sanityissue/cpx]# curl -L google.com
<!doctype html><html itemscope="" itemtype="http://schema.org/WebPage" lang="en-IN"><head><meta content="text/html; charset=UTF-8" http-equiv="Content-Type"><meta content="/images/branding/googleg/1x/g
oogleg_standard_color_128dp.png" itemprop="image"><title>Google</title><script>(function(){window.google={kEI:'ynQwWrr0IcjqvgSE3qLoAg',kEXPI:'18167,1352552,1354276,1354688,1354916,1355005,1355176,13556
74,1355793,1355923,1356020,1356702,1356707,3700328,3700496,3700519,3700521,4003510,4029815,4031109,4043492,4045841,4048347,4076999,4078430,4081039,4081164,4081585,4097153,4097922,4097929,4098721,409872
8,4098752,4101430,4101437,4102237,4103473,4103845,4103861,4104258,4109316,4109490,4110287,4112243,4113216,4114597,4115697,4116351,4116724,4116731,4116926,4116928,4116935,4117328,4117980,4118798,4119032
,4119034,4119036,4120660,4121174,4121518,4122511,4123645,4124091,4124850,4125837,4126206,4126754,4127262,4127418,4127473,4127744,4127863,4128381,4128586,4128624,4129001,4129555,4129633,4130560,4131073,
4131247,4131834,4131853,4132125,4132956,4133090,4133114,4133415,4134398,4135088,4135212,4135249,4135276,4135576,4135744,4135854,4135927,4135934,4136073,4136092,4136136,4137098,4137467,4137597,4137646,4
138246,4138341,4138853,4139471,4139701,4139928,4139935,4139970,4140031,4140104,4141049,4141241,4141445,4141706,4141916,4142235,4142328,4142420,4142492,4142503,4142678,4142729,4142829,4142836,4142847,41
43278,4143295,4143440,4143527,4143901,4144342,4144550,4144732,4144802,4145069,4145088,4145103,4145154,4145174,4145186,4145461,4145485,4145615,4145687,4145742,4145953,4146060,4146452,4146456,4147032,651
2307,10200083,10202524,10202562,15807764,19000288,19000423,19000427,19001977,19001999,19002244,19002245,19002252,19002257,19002548,19002880,19003319,19003321,19003323,19003325,19003326,19003328,1900332
9,19003330,19003407,19003408,19003409,19003919,19004102,19004199,19004201,19004305,19004306,19004309,19004348,19004411,19004425,19004428,19004434,19004440,19004444,41317155',authuser:0,kscs:'c9c918f0_y
nQwWrr0IcjqvgSE3qLoAg',u:'c9c918f0',kGL:'IN'};google.kHL='en-IN';})();(function(){google.lc=[];google.li=0;google.getEI=function(a){for(var b;a&&(!a.getAttribute||!(b=a.getAttribute("eid")));)a=a.paren
tNode;return b||google.kEI};google.getLEI=function(a){for(var b=null;a&&(!a.getAttribute||!(b=a.getAttribute("leid")));)a=a.parentNode;return b};google.https=function(){return"https:"==window.location.
protocol};google.ml=function(){return null};google.wl=function(a,b){try{google.ml(Error(a),!1,b)}catch(d){}};google.time=function(){return(new Date).getTime()};google.log=function(a,b,d,c,g){if(a=googl
e.logUrl(a,b,d,c,g)){b=new Image;var e=google.lc,f=google.li;e[f]=b;b.onerror=b.onload=b.onabort=function(){delete e[f]};google.vel&&google.vel.lu&&google.vel.lu(a);b.src=a;google.li=f+1}};google.logUr
l=function(a,b,d,c,g){var e="",f=google.ls||"";d||-1!=b.search("&ei=")||(e="&ei="+google.getEI(c),-1==b.search("&lei=")&&(c=google.getLEI(c))&&(e+="&lei="+c));c="";!d&&google.cshid&&-1==b.search("&cshi
d=")&&(c="&cshid="+google.cshid);a=d||"/"+(g||"gen_204")+"?atyp=i&ct="+a+"&cad="+b+e+f+"&zx="+google.time()+c;/^http:/i.test(a)&&google.https()&&(google.ml(Error("a"),!1,{src:a,glmm:1}),a="");return a}
;}).call(this);(function(){google.y={};google.x=function(a,b){if(a)var c=a.id;else{do c=Math.random();while(google.y[c])}google.y[c]=[a,b];return!1};google.lm=[];google.plm=function(a){google.lm.push.a
pply(google.lm,a)};google.lq=[];google.load=function(a,b,c){google.lq.push([[a],b,c])};google.loadAll=function(a,b){google.lq.push([a,b])};}).call(this);google.f={};var a=window.location,b=a.href.index
Of("#");if(0<=b){var c=a.href.substring(b+1);/(^|&)q=/.test(c)&&-1==c.indexOf("#")&&a.replace("/search?"+c.replace(/(^|&)fp=[^&]*/g,"")+"&cad=h")};</script><style>#gbar,#guser{font-size:13px;padding-top:1px !important;}#gbar{height:22px}#guser{padding-bottom:7px !important;text-align:right}.gbh,.gbd{border-top:1px solid #c9d7f1;font-size:1px}.gbh{height:0;position:absolute;top:24px;width:100%}@media all{.gb1{height:22px;margin-right:.5em;vertical-align:top}#gbar{float:left}}a.gb1,a.gb4{text-decoration:underline !important}a.gb1,a.gb4{color:#00c !important}.gbi .gb4{color:#dd8e27 !important}.gbf .gb4{color:#900 !important}
Method to know owner of a file
Method to know owner of a file
use stat command
Text Box
dk@7c283c259996:~$ stat test
File: 'test'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 36h/54d Inode: 4393 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2018-02-10 15:17:45.919215000 +0000
Modify: 2018-02-10 15:17:45.919215000 +0000
Change: 2018-02-10 15:17:45.919215000 +0000
Birth: -
dk@7c283c259996:~$ cat test
dk@7c283c259996:~$ echo abcd > test
-bash: test: Permission denied
dk@7c283c259996:~$ id
uid=1001(dk) gid=1001(dk) groups=1001(dk)
dk@7c283c259996:~$
Method to know user of a running process
Method to know user of a running process
use ps -aef
Know owner of a process
dk@7c283c259996:~$ ps -aef | grep nsppe
root 109 1 2 15:11 ? 00:00:23 /var/netscaler/bins/nsppe 1
dk 467 429 0 15:29 pts/0 00:00:00 grep --color=auto nsppe
dk@7c283c259996:~$ id
uid=1001(dk) gid=1001(dk) groups=1001(dk)
dk@7c283c259996:~$ whoami
dk
dk@7c283c259996:~$
Method to get diff of two folders
Method to get diff of two folders
using diff to find difference between two folders
# diff -rq netscaler/triton cpx/netscaler/triton
Files netscaler/triton/nstriton.py and cpx/netscaler/triton/nstriton.py differ
Only in netscaler/triton: test
# touch netscaler/triton/test2
root@master:/var/triton/wkg/cpx/temp# diff -rq netscaler/triton cpx/netscaler/triton
Files netscaler/triton/nstriton.py and cpx/netscaler/triton/nstriton.py differ
Only in netscaler/triton: test
Only in netscaler/triton: test2
Useful link: https://stackoverflow.com/questions/16787916/difference-between-two-directories-in-linux
Know number of threads in a process
Know number of threads in a process
ps -hH -p <process id>
Refer: https://www.tutorialspoint.com/count-the-number-of-threads-in-a-process-on-linux
Reference
Reference
Strace output
https://linux.die.net/man/2/brk
https://linux.die.net/man/2/mprotect
https://linux.die.net/man/2/wait4
https://linux.die.net/man/2/stat
http://askubuntu.com/questions/257248/how-can-i-see-how-many-processor-cores-are-working
https://linux.die.net/man/1/taskset
http://stackoverflow.com/questions/14735010/how-do-you-get-gccs-builtin-frame-address-to-work-with-o2
http://man7.org/linux/man-pages/man3/daemon.3.html
http://man7.org/linux/man-pages/man3/atexit.3.html
http://stackoverflow.com/questions/397075/what-is-the-difference-between-exit-and-abort
http://askubuntu.com/questions/175739/how-do-i-remount-a-filesystem-as-read-write
https://linux.die.net/man/1/ccache
http://stackoverflow.com/questions/3740379/how-can-i-get-the-architecture-of-a-a-file
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/5/html/Tuning_and_Optimizing_Red_Hat_Enterprise_Linux_for_Oracle_9i_and_10g_Databases/chap-Oracle_9i_and_10g_Tuning_Guide-Setting_Shared_Memory.html
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