How to check diskspace and memory usage on a linux (Debian/Ubuntu) computers
To check diskspace
df - Th |
To view a more readable list
du -sh * |
To check memory usage
cat /proc/meminfo |
Tag: Linux
Some more Frequently used SSH commands
We’ve put together some of the more frequently used SSH commands or linux shell commands, and organized them by name so you can easily find a command, their description and how to use it. This guide will continue to be updated and should not be considered a complete list of SSH commands or linux shell commands, but commands, we found, often used. If you would like to add to this guide, please email us and let us know.
Common SSH Commands or Linux Shell Commands,
ls : list files/directories in a directory, comparable to dir in windows/dos.
ls -al : shows all files (including ones that start with a period), directories, and details attributes for each file.
cd : change directory · · cd /usr/local/apache : go to /usr/local/apache/ directory
cd ~ : go to your home directory
cd – : go to the last directory you were in
cd .. : go up a directory cat : print file contents to the screen
cat filename.txt : cat the contents of filename.txt to your screen
chmod: changes file access permissions
The set of 3 go in this order from left to right:
USER – GROUP – EVERONE
0 = --- No permission
1 = --X Execute only
2 = -W- Write only
3 = -WX Write and execute
4 = R-- Read only
5 = R-X Read and execute
6 = RW- Read and write
7 = RWX Read, write and execute
Usage:
chmod numberpermissions filename
chmod 000 : No one can access
chmod 644: Usually for HTML pages
chmod 755: Usually for CGI scripts
chown: changes file ownership permissions
The set of 2 go in this order from left to right:
USER – GROUP
chown root myfile.txt : Changes the owner of the file to root
chown root.root myfile.txt : Changes the owner and group of the file to root
tail : like cat, but only reads the end of the file
tail /var/log/messages : see the last 20 (by default) lines of /var/log/messages
tail -f /var/log/messages : watch the file continuously, while it’s being updated
tail -200 /var/log/messages : print the last 200 lines of the file to the screen
more : like cat, but opens the file one screen at a time rather than all at once
more /etc/userdomains : browse through the userdomains file. hit Spaceto go to the next page, q to quit
pico : friendly, easy to use file editor
pico /home/burst/public_html/index.html : edit the index page for the user’s website.
File Editing with VI ssh commands
vi : another editor, tons of features, harder to use at first than pico
vi /home/burst/public_html/index.html : edit the index page for the user’s website.
Whie in the vi program you can use the following useful commands, you will need to hit SHIFT + : to go into command mode
:q! : This force quits the file without saving and exits vi
:w : This writes the file to disk, saves it
:wq : This saves the file to disk and exists vi
:LINENUMBER : EG :25 : Takes you to line 25 within the file
:$ : Takes you to the last line of the file
:0 : Takes you to the first line of the file
grep : looks for patterns in files
grep root /etc/passwd : shows all matches of root in /etc/passwd
grep -v root /etc/passwd : shows all lines that do not match root
ln : create’s “links” between files and directories
ln -s /usr/local/apache/conf/httpd.conf /etc/httpd.conf : Now you can edit /etc/httpd.conf rather than the original. changes will affect the orginal, however you can delete the link and it will not delete the original.
last : shows who logged in and when
last -20 : shows only the last 20 logins
last -20 -a : shows last 20 logins, with the hostname in the last field
w : shows who is currently logged in and where they are logged in from.
who : This also shows who is on the server in an shell.
netstat : shows all current network connections.
netstat -an : shows all connections to the server, the source and destination ips and ports.
netstat -rn : shows routing table for all ips bound to the server.
top : shows live system processes in a nice table, memory information, uptime and other useful info. This is excellent for managing your system processes, resources and ensure everything is working fine and your server isn’t bogged down.
top then type Shift + M to sort by memory usage or Shift + P to sort by CPU usage
ps: ps is short for process status, which is similar to the top command. It’s used to show currently running processes and their PID.
A process ID is a unique number that identifies a process, with that you can kill or terminate a running program on your server (see kill command).
ps U username : shows processes for a certain user
ps aux : shows all system processes
ps aux –forest : shows all system processes like the above but organizes in a hierarchy that’s very useful!
touch : create an empty file
touch /home/burst/public_html/404.html : create an empty file called 404.html in the directory /home/burst/public_html/
file : attempts to guess what type of file a file is by looking at it’s content.
file * : prints out a list of all files/directories in a directory
du : shows disk usage.
du -sh : shows a summary, in human-readble form, of total disk space used in the current directory, including subdirectories.
du -sh * : same thing, but for each file and directory. helpful when finding large files taking up space.
wc : word count
wc -l filename.txt : tells how many lines are in filename.txt
cp : copy a file
cp filename filename.backup : copies filename to filename.backup
cp -a /home/burst/new_design/* /home/burst/public_html/ : copies all files, retaining permissions form one directory to another.
cp -av * ../newdir : Copies all files and directories recurrsively in the current directory INTO newdir
mv : Move a file command
mv oldfilename newfilename : Move a file or directory from oldfilename to newfilename
rm : delete a file
rm filename.txt : deletes filename.txt, will more than likely ask if you really want to delete it
rm -f filename.txt : deletes filename.txt, will not ask for confirmation before deleting.
rm -rf tmp/ : recursively deletes the directory tmp, and all files in it, including subdirectories. BE VERY CAREFULL WITH THIS COMMAND!!!
TAR: Creating and Extracting .tar.gz and .tar files
tar -zxvf file.tar.gz : Extracts the file
tar -xvf file.tar : Extracts the file
tar -cf archive.tar contents/ : Takes everything from contents/ and puts it into archive.tar
gzip -d filename.gz : Decompress the file, extract it
ZIP Files: Extracting .zip files shell command
unzip file.zip
Firewall – iptables commands
iptables -I INPUT -s IPADDRESSHERE -j DROP : This command stops any connections from the IP address
iptables -L : List all rules in iptables
iptables -F : Flushes all iptables rules (clears the firewall)
iptables –save : Saves the currenty ruleset in memory to disk
service iptables restart : Restarts iptables
Apache Shell Commands
httpd -v : Outputs the build date and version of the Apache server.
httpd -l : Lists compiled in Apache modules
httpd status : Only works if mod_status is enabled and shows a page of active connections
service httpd restart : Restarted Apache web server
MySQL Shell Commands
mysqladmin processlist : Shows active mysql connections and queries
mysqladmin drop databasenamehere : Drops/deletes the selected database
mysqladmin create databasenamehere : Creates a mysql database
Restore MySQL Database Shell Command
mysql -u username -p password databasename < databasefile.sql : Restores a MySQL database from databasefile.sql
Backup MySQL Database Shell Command
mysqldump -u username -p password databasename > databasefile.sql : Backup MySQL database to databasefile.sql
kill: terminate a system process
kill -9 PID EG: kill -9 431
kill PID EG: kill 10550
Use top or ps ux to get system PIDs (Process IDs)
EG:
| PID | TTY | TIME | COMMAND |
| 10550 | pts/3 | 0:01 | /bin/csh |
| 10574 | pts/4 | 0:02 | /bin/csh |
| 10590 | pts/4 | 0:09 | APP |
Each line represents one process, with a process being loosely defined as a running instance of a program. The column headed PID (process ID) shows the assigned process numbers of the processes. The heading COMMAND shows the location of the executed process.
Putting commands together
Often you will find you need to use different commands on the same line. Here are some examples. Note that the | character is called a pipe, it takes date from one program and pipes it to another.
> means create a new file, overwriting any content already there.
>> means tp append data to a file, creating a newone if it doesn not already exist.
< send input from a file back into a command.
grep User /usr/local/apache/conf/httpd.conf |more
This will dump all lines that match User from the httpd.conf, then print the results to your screen one page at a time.
last -a > /root/lastlogins.tmp
This will print all the current login history to a file called lastlogins.tmp in /root/
tail -10000 /var/log/exim_mainlog |grep domain.com |more
This will grab the last 10,000 lines from /var/log/exim_mainlog, find all occurances of domain.com (the period represents ‘anything’,
— comment it out with a so it will be interpretted literally), then send it to your screen page by page.
netstat -an |grep :80 |wc -l
Show how many active connections there are to apache (httpd runs on port 80)
mysqladmin processlist |wc -l
Show how many current open connections there are to mysql
Search for files using SSH
To search the current directory and all subdirectories for a folder or file, use the following command:
find . -name filename |
– where filename is the file or folder for which you are looking…
To search one directory and all its subdirectories use the following command:
find foldername -name filename |
– where filename is the file or folder for which you are looking and foldername is the folder in which you want to search.
To search for files containing a string
grep -ir search_string * |
– i denotes case insensitive and r is for recursive
To count number of files in a directory
ls -ral | grep '-' -c |
Recursively modify permissions
It might look all that simple, but it took me a while to figure out. The following command looks for directories and sets the permission to 777. First you need to ch into the directory and change them from there.
If you’re installing SugarCRM you are required to set the entire directories as well as files under modules directory to writable. Go on now.
Common Shell Commands
| cd [directory] | The cd command changes your current working directory to the directory you specify.
Example: % cd ~/www/htdocs/ |
|---|---|
| pwd | The pwd command prints your current (or present) working directory. Simply type pwd and hit return to display your current working directory.Example: % pwd |
| ls [directory] | The ls command is used to list the file in the directory specified, or if you do not specify a directory, the current working directory. You can also add some additional arguments to customize the list display.If you type ls -F it will append a forward slash to the subdirectory names so you can easily distinguish them from file names. If you type ls -a it will show all hidden files. Hidden files begin with a dot If you type ls -l it will show detailed information about each file and directory, You can also mix the arguments. If you type ls -aF you will see a list of all file Example: % ls -al |
| cat [filename] | The cat command displays the contents of filename. If you want to display the file one screen at a time try cat [filename] | more or simply more [filename].Example: % cat ~/var/log/messages |
| mkdir [directory] | The mkdir command makes a new directory with the name directory, that you specify.
Example: % mkdir myfiles |
| rmdir [directory] | The rmdir command removes the directory that you specify.
Example: % rmdir myfiles |
| cp [source-file] [target-file] | The cp command creates a copy of source-file with the name target-file. You can specify pathnames as part of the file specification. If target-file exists it is overwritten.Example: % cp index.html ~/www/htdocs/index.html |
| mv [source-file] [target-file] | The mv command renames a file or moves it to a new location. You can specify pathnames as part of the file specification. If target-file exists it is overwritten.Example: % mv ~/www/htdocs/index.html ~/www/vhosts/mydomain/index.html |
| rm [filename] | The rm command deletes (removes) a file.To remove a directory and eveyrthing inside, you can use the -r (recursive) flag (e.g. rm -r filename).You can specify pathnames as part of the file name specification.Example: % rm ~/www/htdocs/old-index.html |
| grep [pattern] [filenames] | The grep command finds lines in files that match specified text patterns. You can specify pathnames as part of the file specification. For example if you want to search for the pattern gif in all html files in your current working directory, you would type grep gif *.html and hit return. The grep command would then list all occurrences of gif it finds in .html files in the current working directory.Example: % grep href *.html |
| tar [options] [tarfile] [files] | The tar command copies a file or files to or from an archive. To put all the files in a directory into one tar format file, simply type tar -cvf tarfile directory at a telnet command prompt and replace tarfile with the name you want to call your archived file, and replace directory with the name of the directory that contains the files you want to compress.To extract the files from a tar format archive, simply type tar -xvf tarfile at a telnet command prompt and replace tarfile with the name of the archived file you are extracting. For example, you could type tar -cvf pages.tar htdocs at a telnet command prompt to Example: % tar -cvf mysite.tar ~/www/htdocs/ |
| zip [options] [zipfile] [files] | The zip command compresses a file or list of files into a zip format archive file. Zip files are a common archive format used on PCs (using programs such as PKZip or WinZip), so the zip utiltity is ideal to compress large files or several files for transfer between your Virtual Private Server and your PC. Adding -r attribute recursively adds Example: % zip mysite.zip ~/www/htdocs/ % zip -r mysite.zip * |
| unzip [options] [zipfile] | unzip extracts the contents of a zip file made using the zip command or using WinZip or PKZip on your PC.Example: % unzip mysite.zip ~/www/htdocs/ |
| du [options] [path] | du displays the disk usage / directory size for the specified path The options -hs provides human readable summary. Example: % du -hs ~/www/htdocs/ |