Linux Useful Commands

Posted: May 23, 2019 in Uncategorized
List of Linux commands – Useful to regular job
SNO
Context
Command
Notes
Reference
1
Sum of files in a directory
du -ach *
Total size of files is shown at the bottom of the output along with individual file size
2
Grep a string in dir and sub dir
1. grep -R ‘string’ dir/
2. find dir/ -type f -exec grep -H ‘string’ {} +
3
Convert date in squid log
perl -pe ‘s/\d+/localtime($&)/e’ access.log
Squid access.log generally shows in a format of 1178695088.774. This helps to convert it in readable time manner
4
Logs between 2 time stamps
sed -n ‘/Feb 12 00:00:02/,/Feb 14 23:59:59/P’ access.log
5
Count the no’of occurance in a file
grep -o ‘503’ access.log |wc -l
6
Count the time_wait in server
netstat -aon | grep tcp | grep TIME_WAIT | wc -l
7
Search for error codes
zgrep -P ‘\t503\t’ access_log.20190213* |wc –
To search in zip/archived files
8
S3 bucket/object size
aws s3 ls s3://Bucket-name/ –recursive –human-readable –summarize
9
Curl output with timestamp of reqeuest time with new line prints
curl -s –insecure -L -X GET -A “ios” –proxy 2.3.4.1:8080 https://wgetip.com -w “\n” | ts ‘[%Y-%m-%d %H:%M:%S]’
10
Internet speed test through CLI
For Installation: Download – tool
2. chmod +x speedtest-cli
3. ./speedtest-cli
11
tcpdump
tcpdump -c 8 -tttt -i eth0 -w tcpdump-8080.pcap port 8080
12
sbt – package installation
2. yum install sbt-0.13.5.rpm
SBT – Scala Build Tool – Required for make create on credit stack of iOS proxy
13
Compare 2 files and print matched data
awk ‘NR==FNR{a[$0];next} ($0 in a)’ file1.out file2.out
14
netstat -s
15
netstat -ant | awk ‘{print $6}’ | sort | uniq -c | sort -n
16
History with date
1. export HISTTIMEFORMAT=’%F %t ‘
2. history
17
sbt version
sbt sbtVersion
18
Search for a string/text in multiple files
grep -rnw ‘/etc/datadog-agent/’ -e ‘squid’
19
Extract field based data from a file
awk ‘{print $1}’ filename.txt
Prints column field in a file
20
Print full line of a file based on search field criteria
awk ‘$3 == “11903” { print $0 }’ log.txt
It prints whole line of a file where ever it has the string value
$3 -> For 3rd field/column
print $0 -> to print whole line
21
Prints uniq data from a file
awk ‘{print $3} log.txt | sort | uniq
print 3rd column/field
22
Service monitoring
if service is down, it restarts automatically
23
Extract 2nd column from a file (Usecase: Log file )
awk ‘{print $2}’ error.log > error.out
Extract and print in other file
24
Print only the chars/string after a delimiter
awk -F’.’ ‘{print $1,$2,$3}’ OFS=’.’ error.log
Prints only 1st ($1), 2nd and 3rd chars after a delimiter .
25
Print number of occurrences in a file while checking the string/char/pattern in one file
awk ‘NR==FNR{arr[$0];next} $0 in arr’ file1 file2 | sort | uniq -c
It reads line by line in File1 and compare it with File2. If matches prints number of occurrences in File2
26
Find files with 0 size and delete them all from a directory
  1. find . -type f -size 0 -delete
  2. find ./ -type f -size 0 | xargs rm -f
  3. find ./ -type f -size 0 -exec rm -f {} \;

 

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