Linux Commands Reference

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Command Description
System information & Details
# arch show architecture of machine
# cal 2007 show the timetable of 2007
# cat /proc/cpuinfo show information CPU info
# cat /proc/interrupts show interrupts
# cat /proc/meminfo verify memory use
# cat /proc/swaps show file(s) swap
# cat /proc/version show version of the kernel
# cat /proc/net/dev show network adpters and statistics
# cat /proc/mounts show mounted file system(s)
# clock -w save date changes on BIOS
# date show system date
# date 041217002007.00 set date and time - MonthDayhoursMinutesYear.Seconds
# dmidecode -q show hardware system components - (SMBIOS / DMI)
# hdparm -i /dev/hda displays the characteristics of a hard-disk
# hdparm -tT /dev/sda perform test reading on a hard-disk
# lspci -tv display PCI devices
# lsusb -tv show USB devices
# uname -m show architecture of machine
# uname -r show used kernel version
Shutdown, Restart and Logout of a system
# init 0 shutdown system
# logout leaving session
# reboot reboot
# shutdown -h now shutdown system
# shutdown -h 16:30 & planned shutdown of the system at 16:30
# shutdown -c cancel a planned shutdown of the system
# shutdown -r now reboot
# telinit 0 shutdown system
Files and Directory
# cd /home enter to directory '/ home'
# cd .. go back one level
# cd ../.. go back two levels
# cd go to home directory
# cd ~user1 go to home directory
# cd - go to previous directory
# cp file1 file2 copying a file
# cp dir/* . copy all files of a directory within the current work directory
# cp -a /tmp/dir1 . copy a directory within the current work directory
# cp -a dir1 dir2 copy a directory
# cp file file1 outputs the mime type of the file as text
# iconv -l lists known encodings
# iconv -f fromEncoding -t toEncoding inputFile > outputFile converting the coding of characters from one format to another
# find . -maxdepth 1 -name *.jpg -print -exec convert batch resize files in the current directory and send them to a thumbnails directory (requires convert from Imagemagick)
# ln -s file1 lnk1 create a symbolic link to file or directory
# ln file1 lnk1 create a physical link to file or directory
# ls view files of directory
# ls -F view files of directory
# ls -l show details of files and directory
# ls -a show hidden files
# ls *[0-9]* show files and directory containing numbers
# lstree show files and directories in a tree starting from root(2)
# mkdir dir1 create a directory called 'dir1'
# mkdir dir1 dir2 create two directories simultaneously
# mkdir -p /tmp/dir1/dir2 create a directory tree
# mv dir1 new_dir rename / move a file or directory
# pwd show the path of work directory
# rm -f file1 delete file called 'file1'
# rm -rf dir1 remove a directory called 'dir1' and contents recursively
# rm -rf dir1 dir2 remove two directories and their contents recursively
# rmdir dir1 delete directory called 'dir1'
# touch -t 0712250000 file1 modify timestamp of a file or directory - (YYMMDDhhmm)
# tree show files and directories in a tree starting from root(1)
File search
# find / -name file1 search file and directory into root filesystem from '/'
# find / -user user1 search files and directories belonging to 'user1'
# find /home/user1 -name \*.bin search files with '. bin' extension within directory '/ home/user1'
# find /usr/bin -type f -atime +100 search binary files are not used in the last 100 days
# find /usr/bin -type f -mtime -10 search files created or changed within 10 days
# find / -name *.rpm -exec chmod 755 '{}' \; search files with '.rpm' extension and modify permits
# find / -xdev -name \*.rpm search files with '.rpm' extension ignoring removable partitions as cdrom, pen-drive, etc.…
# locate \*.ps find files with the '.ps' extension - first run 'updatedb' command
# whereis halt show location of a binary file, source or man
# which halt show full path to a binary / executable
Mounting a Filesystem
# fuser -km /mnt/hda2 force umount when the device is busy
# mount /dev/hda2 /mnt/hda2 mount disk called hda2 - verify existence of the directory '/ mnt/hda2'
# mount /dev/fd0 /mnt/floppy mount a floppy disk
# mount /dev/cdrom /mnt/cdrom mount a cdrom / dvdrom
# mount /dev/hdc /mnt/cdrecorder mount a cdrw / dvdrom
# mount /dev/hdb /mnt/cdrecorder mount a cdrw / dvdrom
# mount -o loop file.iso /mnt/cdrom mount a file or iso image
# mount -t vfat /dev/hda5 /mnt/hda5 mount a Windows FAT32 file system
# mount /dev/sda1 /mnt/usbdisk mount a usb pen-drive or flash-drive
# mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share mount a windows network share
# umount /dev/hda2 unmount disk called hda2 - exit from mount point '/ mnt/hda2' first
# umount -n /mnt/hda2 run umount without writing the file /etc/mtab - useful when the file is read-only or the hard disk is full
Disk Space
# df -h show list of partitions mounted
# dpkg-query -W -f='${Installed-Size;10}t${Package}n' | sort -k1,1n show the used space by installed deb packages, sorting by size (debian, ubuntu and alike)
# du -sh dir1 estimate space used by directory 'dir1'
# du -sk * | sort -rn show size of the files and directories sorted by size
# ls -lSr |more show size of the files and directories ordered by size
# rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n show the used space by rpm packages installed sorted by size (fedora, redhat and alike)
Networking (LAN / WiFi)
# dhclient eth0 active interface 'eth0' in dhcp mode
# ethtool eth0 show network statistics of eth0
# host www.example.com lookup hostname to resolve name to ip address and viceversa
# hostname show hostname of system
# ifconfig eth0 show configuration of an ethernet network card
# ifconfig eth0 192.168.1.1 netmask 255.255.255.0 configure IP Address
# ifconfig eth0 promisc configure 'eth0' in promiscuous mode to gather packets (sniffing)
# ifdown eth0 disable an interface 'eth0'
# ifup eth0 activate an interface 'eth0'
# ip link show show link status of all network interfaces
# iwconfig eth1 show wireless networks
# iwlist scan wifi scanning to display the wireless connections available
# mii-tool eth0 show link status of 'eth0'
# netstat -tup show all active network connections and their PID
# netstat -tupl show all network services listening on the system and their PID
# netstat -rn show routing table alike "route -n"
# nslookup www.example.com lookup hostname to resolve name to ip address and viceversa
# route -n show routing table
# route add -net 0/0 gw IP_Gateway configure default gateway
# route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1 configure static route to reach network '192.168.0.0/16'
# route del 0/0 gw IP_gateway remove static route
# echo "1" > /proc/sys/net/ipv4/ip_forward activate ip routing temporarily
# tcpdump tcp port 80 show all HTTP traffic
# whois www.example.com lookup on Whois database
Users and Groups
# chage -E 2005-12-31 user1 set deadline for user password
# groupadd [group] create a new group
# groupdel [group] delete a group
# groupmod -n moon sun rename a group from moon to sun
# grpck check correct syntax and file format of '/etc/group' and groups existence
# newgrp - [group] log into a new group to change default group of newly created files
# passwd change password
# passwd user1 change a user password (only by root)
# pwck check correct syntax and file format of '/etc/passwd' and users existence
# useradd -c "User Linux" -g admin -d /home/user1 -s /bin/bash user1 create a new user "user1" belongs "admin" group
# useradd user1 create a new user
# userdel -r user1 delete a user ( '-r' eliminates home directory)
# usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 change user attributes as description, group and other
Permits on Files
# chgrp group1 file1 change group of files
# chmod ugo+rwx directory1 set permissions reading (r), write (w) and (x) access to users owner (u) group (g) and others (o)
# chmod go-rwx directory1 remove permits reading (r), write (w) and (x) access to users group (g) and others (or
# chmod u+s /bin/file1 set SUID bit on a binary file - the user that running that file gets same privileges as owner
# chmod u-s /bin/file1 disable SUID bit on a binary file
# chmod g+s /home/public set SGID bit on a directory - similar to SUID but for directory
# chmod g-s /home/public disable SGID bit on a directory
# chmod o+t /home/public set STIKY bit on a directory - allows files deletion only to legitimate owners
# chmod o-t /home/public disable STIKY bit on a directory
# chown user1 file1 change owner of a file
# chown -R user1 directory1 change user owner of a directory and all the files and directories contained inside
# chown user1:group1 file1 change user and group ownership of a file
# find / -perm -u+s view all files on the system with SUID configured
# ls -lh show permits on files
# ls /tmp | pr -T5 -W$COLUMNS divide terminal into 5 columns
Special Attributes on files
# chattr +a file1 allows write opening of a file only append mode
# chattr +c file1 allows that a file is compressed / decompressed automatically by the kernel
# chattr +d file1 makes sure that the program ignores Dump the files during backup
# chattr +i file1 makes it an immutable file, which can not be removed, altered, renamed or linked
# chattr +s file1 allows a file to be deleted safely
# chattr +S file1 makes sure that if a file is modified changes are written in synchronous mode as with sync
# chattr +u file1 allows you to recover the contents of a file even if it is canceled
# lsattr show specials attributes
Archives and compressed files
# bunzip2 file1.bz2 decompress a file called 'file1.bz2'
# bzip2 file1 compress a file called 'file1'
# gunzip file1.gz decompress a file called 'file1.gz'
# gzip file1 compress a file called 'file1'
# gzip -9 file1 compress with maximum compression
# rar a file1.rar test_file create an archive rar called 'file1.rar'
# rar a file1.rar file1 file2 dir1 compress 'file1', 'file2' and 'dir1' simultaneously
# rar x file1.rar decompress rar archive
# tar -cvf archive.tar file1 create a uncompressed tarball
# tar -cvf archive.tar file1 file2 dir1 create an archive containing 'file1', 'file2' and 'dir1'
# tar -tf archive.tar show contents of an archive
# tar -xvf archive.tar extract a tarball
# tar -xvf archive.tar -C /tmp extract a tarball into / tmp
# tar -cvfj archive.tar.bz2 dir1 create a tarball compressed into bzip2
# tar -xvfj archive.tar.bz2 decompress a compressed tar archive in bzip2
# tar -cvfz archive.tar.gz dir1 create a tarball compressed into gzip
# tar -xvfz archive.tar.gz decompress a compressed tar archive in gzip
# unrar x file1.rar decompress rar archive
# unzip file1.zip decompress a zip archive
# zip file1.zip file1 create an archive compressed in zip
# zip -r file1.zip file1 file2 dir1 compress in zip several files and directories simultaneously
RPM Packages ( Fedora, Red Hat and like)
# rpm -ivh [package.rpm] install a rpm package
# rpm -ivh --nodeeps [package.rpm] install a rpm package ignoring dependencies requests
# rpm -U [package.rpm] upgrade a rpm package without changing configuration files
# rpm -F [package.rpm] upgrade a rpm package only if it is already installed
# rpm -e [package] remove a rpm package
# rpm -qa show all rpm packages installed on the system
# rpm -qa | grep httpd show all rpm packages with the name "httpd"
# rpm -qi [package] obtain information on a specific package installed
# rpm -qg "System Environment/Daemons" show rpm packages of a group software
# rpm -ql [package] show list of files provided by a rpm package installed
# rpm -qc [package] show list of configuration files provided by a rpm package installed
# rpm -q [package] --whatrequires show list of dependencies required for a rpm packet
# rpm -q [package] --whatprovides show capability provided by a rpm package
# rpm -q [package] --scripts show scripts started during installation / removal
# rpm -q [package] --changelog show history of revisions of a rpm package
# rpm -qf /etc/httpd/conf/httpd.conf verify which rpm package belongs to a given file
# rpm -qp [package.rpm] -l show list of files provided by a rpm package not yet installed
# rpm --import /media/cdrom/RPM-GPG-KEY import public-key digital signature
# rpm --checksig [package.rpm] verify the integrity of a rpm package
# rpm -qa gpg-pubkey verify integrity of all rpm packages installed
# rpm -V [package] check file size, permissions, type, owner, group, MD5 checksum and last modification
# rpm -Va check all rpm packages installed on the system - use with caution
# rpm -Vp [package.rpm] verify a rpm package not yet installed
# rpm -ivh /usr/src/redhat/RPMS/`arch`/[package.rpm] install a package built from a rpm source
# rpm2cpio [package.rpm] | cpio --extract --make-directories *bin* extract executable file from a rpm package
# rpmbuild --rebuild [package.src.rpm] build a rpm package from a rpm source
YUM packages tool (Fedora, RedHat and alike)
# yum -y install [package] download and install a rpm package
# yum localinstall [package.rpm] That will install an RPM, and try to resolve all the dependencies for you using your repositories.
# yum -y update update all rpm packages installed on the system
# yum update [package] upgrade a rpm package
# yum remove [package] remove a rpm package
# yum list list all packages installed on the system
# yum search [package] find a package on rpm repository
# yum clean [package] clean up rpm cache erasing downloaded packages
# yum clean headers remove all files headers that the system uses to resolve dependency
# yum clean all remove from the cache packages and headers files
DEB packages (Debian, Ubuntu and like)
# dpkg -i [package.deb] install / upgrade a deb package
# dpkg -r [package] remove a deb package from the system
# dpkg -l show all deb packages installed on the system
# dpkg -l | grep httpd show all deb packages with the name "httpd"
# dpkg -s [package] obtain information on a specific package installed on system
# dpkg -L [package] show list of files provided by a package installed on system
# dpkg --contents [package.deb] show list of files provided by a package not yet installed
# dpkg -S /bin/ping verify which package belongs to a given file
APT packages tool (Debian, Ubuntu and alike)
# apt-cache search [package] returns list of packages which corresponds string "searched-packages"
# apt-cdrom install [package] install / upgrade a deb package from cdrom
# apt-get install [package] install / upgrade a deb package
# apt-get update update the package list
# apt-get upgrade upgrade all of the installed packages
# apt-get remove [package] remove a deb package from system
# apt-get check verify correct resolution of dependencies
# apt-get clean clean up cache from packages downloaded
Pacman packages tool (Arch, Frugalware and alike)
# pacman -S name Install package 'name' with dependencies
# pacman -R name Delete package 'name' and all files of it
View file content
# cat file1 view the contents of a file starting from the first row
# head -2 file1 view first two lines of a file
# less file1 similar to 'more' command but which allows backward movement in the file as well as forward movement
# more file1 view content of a file along
# tac file1 view the contents of a file starting from the last line
# tail -2 file1 view last two lines of a file
# tail -f /var/log/messages view in real time what is added to a file
Text Manipulation
# cat example.txt | awk 'NR%2==1' remove all even lines from example.txt
# echo a b c | awk '{print $1}' view the first column of a line
# echo a b c | awk '{print $1,$3}' view the first and third column of a line
# cat -n file1 number row of a file
# comm -1 file1 file2 compare contents of two files by deleting only unique lines from 'file1'
# comm -2 file1 file2 compare contents of two files by deleting only unique lines from 'file2'
# comm -3 file1 file2 compare contents of two files by deleting only the lines that appear on both files
# diff file1 file2 find differences between two files
# grep Aug /var/log/messages look up words "Aug" on file '/var/log/messages'
# grep ^Aug /var/log/messages look up words that begin with "Aug" on file '/var/log/messages'
# grep [0-9] /var/log/messages select from file '/var/log/messages' all lines that contain numbers
# grep Aug -R /var/log/* search string "Aug" at directory '/var/log' and below
# paste file1 file2 merging contents of two files for columns
# paste -d '+' file1 file2 merging contents of two files for columns with '+' delimiter on the center
# sdiff file1 file2 find differences between two files and merge interactively alike "diff"
# sed 's/string1/string2/g' example.txt replace "string1" with "string2" in example.txt
# sed '/^$/d' example.txt remove all blank lines from example.txt
# sed '/ *#/d; /^$/d' example.txt remove comments and blank lines from example.txt
# sed -e '1d' exampe.txt eliminates the first line from file example.txt
# sed -n '/string1/p' view only lines that contain the word "string1"
# sed -e 's/ *$//' example.txt remove empty characters at the end of each row
# sed -e 's/string1//g' example.txt remove only the word "string1" from text and leave intact all
# sed -n '1,5p' example.txt print from 1th to 5th row of example.txt
# sed -n '5p;5q' example.txt print row number 5 of example.txt
# sed -e 's/00*/0/g' example.txt replace more zeros with a single zero
# sort file1 file2 sort contents of two files
# sort file1 file2 | uniq sort contents of two files omitting lines repeated
# sort file1 file2 | uniq -u sort contents of two files by viewing only unique line
# sort file1 file2 | uniq -d sort contents of two files by viewing only duplicate line
# echo 'word' | tr '[:lower:]' '[:upper:]' convert from lower case in upper case
Character set and Format file conversion
# dos2unix filedos.txt fileunix.txt convert a text file format from MSDOS to UNIX
# recode ..HTML < page.txt > page.html convert a text file to html
# recode -l | more show all available formats conversion
# unix2dos fileunix.txt filedos.txt convert a text file format from UNIX to MSDOS
Filesystem Analysis
# badblocks -v /dev/hda1 check bad blocks on disk hda1
# dosfsck /dev/hda1 repair / check integrity of dos filesystems on disk hda1
# e2fsck /dev/hda1 repair / check integrity of ext2 filesystem on disk hda1
# e2fsck -j /dev/hda1 repair / check integrity of ext3 filesystem on disk hda1
# fsck /dev/hda1 repair / check integrity of linux filesystem on disk hda1
# fsck.ext2 /dev/hda1 repair / check integrity of ext2 filesystem on disk hda1
# fsck.ext3 /dev/hda1 repair / check integrity of ext3 filesystem on disk hda1
# fsck.vfat /dev/hda1 repair / check integrity of fat filesystem on disk hda1
# fsck.msdos /dev/hda1 repair / check integrity of dos filesystem on disk hda1
Format a Filesystem
# fdformat -n /dev/fd0 format a floppy disk
# mke2fs /dev/hda1 create a filesystem type linux ext2 on hda1 partition
# mke2fs -j /dev/hda1 create a filesystem type linux ext3 (journal) on hda1 partition
# mkfs /dev/hda1 create a filesystem type linux on hda1 partition
# mkfs -t vfat 32 -F /dev/hda1 create a FAT32 filesystem
# mkswap /dev/hda3 create a swap filesystem
Filesystem SWAP
# mkswap /dev/hda3 create a swap filesystem
# swapon /dev/hda3 activating a new swap partition
# swapon /dev/hda2 /dev/hdb3 activate two swap partitions
Backup
# find /var/log -name '*.log' | tar cv --files-from=- | bzip2 > log.tar.bz2 find all files with '.log' extention and make an bzip archive
# find /home/user1 -name '*.txt' | xargs cp -av --target-directory=/home/backup/ --parents find and copy all files with '.txt' extention from a directory to another
# dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr 'dd of=hda.gz' make a backup of a local hard disk on remote host via ssh
# dd if=/dev/sda of=/tmp/file1 backup content of the harddrive to a file
# dd if=/dev/hda of=/dev/fd0 bs=512 count=1 make a copy of MBR (Master Boot Record) to floppy
# dd if=/dev/fd0 of=/dev/hda bs=512 count=1 restore MBR from backup copy saved to floppy
# dump -0aj -f /tmp/home0.bak /home make a full backup of directory '/home'
# dump -1aj -f /tmp/home0.bak /home make a incremental backup of directory '/home'
# restore -if /tmp/home0.bak restoring a backup interactively
# rsync -rogpav --delete /home /tmp synchronization between directories
# rsync -rogpav -e ssh --delete /home ip_address:/tmp rsync via SSH tunnel
# rsync -az -e ssh --delete ip_addr:/home/public /home/local synchronize a local directory with a remote directory via ssh and compression
# rsync -az -e ssh --delete /home/local ip_addr:/home/public synchronize a remote directory with a local directory via ssh and compression
# tar -Puf backup.tar /home/user make a incremental backup of directory '/home/user'
# ( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr 'cd /home/share/ && tar x -p' copy content of a directory on remote directory via ssh
# ( tar c /home ) | ssh -C user@ip_addr 'cd /home/backup-home && tar x -p' copy a local directory on remote directory via ssh
# tar cf - . | (cd /tmp/backup ; tar xf - ) local copy preserving permits and links from a directory to another
CDROM
# cd-paranoia -B rip audio tracks from a CD to wav files
# cd-paranoia -- rip first three audio tracks from a CD to wav files
# cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force clean a rewritable cdrom
# cdrecord -v dev=/dev/cdrom cd.iso burn an ISO image
# gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom - burn a compressed ISO image
# cdrecord --scanbus scan bus to identify the channel scsi
# dd if=/dev/hdc | md5sum perform an md5sum on a device, like a CD
# mkisofs /dev/cdrom > cd.iso create an iso image of cdrom on disk
# mkisofs /dev/cdrom | gzip > cd_iso.gz create a compressed iso image of cdrom on disk
# mkisofs -J -allow-leading-dots -R -V create an iso image of a directory
# mount -o loop cd.iso /mnt/iso mount an ISO image
Microsoft Windows networks (samba)
# mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share mount a windows network share
# nbtscan ip_addr netbios name resolution
# nmblookup -A ip_addr netbios name resolution
# smbclient -L ip_addr/hostname show remote shares of a windows host
# smbget -Rr smb://ip_addr/share like wget can download files from a host windows via smb
IPTABLES (firewall)
# iptables -t filter -L show all chains of filtering table
# iptables -t nat -L show all chains of nat table
# iptables -t filter -F clear all rules from filtering table
# iptables -t nat -F clear all rules from table nat
# iptables -t filter -X delete any chains created by user
# iptables -t filter -A INPUT -p tcp --dport telnet -j ACCEPT allow telnet connections to input
# iptables -t filter -A OUTPUT -p tcp --dport http -j DROP block HTTP connections to output
# iptables -t filter -A FORWARD -p tcp --dport pop3 -j ACCEPT allow POP3 connections to forward chain
# iptables -t filter -A INPUT -j LOG --log-prefix Logging on input chain
# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE configure a PAT (Port Address Traslation) on eth0 masking outbound packets
# iptables -t nat -A PREROUTING -d 192.168.0.1 -p tcp -m tcp --dport 22 -j DNAT --to-destination 10.0.0.2:22 redirect packets addressed to a host to another host
Monitoring and debugging
# free -m displays status of RAM in megabytes
# kill -9 process_id force closure of the process and finish it
# kill -1 process_id force a process to reload configuration
# last reboot show history reboot
# lsmod display kernel loaded
# lsof -p process_id display a list of files opened by processes
# lsof /home/user1 displays a list of open files in a given path system
# ps -eafw displays linux tasks
# ps -e -o pid,args --forest displays linux tasks in a hierarchical mode
# pstree Shows a tree system processes
# smartctl -A /dev/hda monitoring reliability of a hard-disk through SMART
# smartctl -i /dev/hda check if SMART is active on a hard-disk
# strace -c ls >/dev/null display system calls made and received by a process
# strace -f -e open ls >/dev/null display library calls
# tail /var/log/dmesg show events inherent to the process of booting kernel
# tail /var/log/messages show system events
# top display linux tasks using most cpu
# watch -n1 'cat /proc/interrupts' display interrupts in real-time
Others useful commands
# alias hh='history' set an alias for a command - hh = history
# apropos ...keyword display a list of commands that pertain to keywords of a program , useful when you know what your program does, but you don't know the name of the command
# chsh change shell command
# chsh --list-shells nice command to know if you have to remote into another box
# gpg -c file1 encrypt a file with GNU Privacy Guard
# gpg file1.gpg decrypt a file with GNU Privacy Guard
# ldd /usr/bin/ssh show shared libraries required by ssh program
# man ping display the on-line manual pages for example on ping command - use '-k' option to find any related commands
# mkbootdisk --device /dev/fd0 `uname -r` create a boot floppy
# wget -r www.example.com download an entire web site
# wget -c www.example.com/file.iso download a file with the ability to stop the download and resume later
# echo 'wget -c www.example.com/files.iso' | at 09:00 start a download at any given time
# whatis ...keyword displays description of what a program does
# who -a show who is logged on, and print: time of last system boot, dead processes, system login processes, active processes spawned by init, current runlevel, last system clock change

Reference : LinuxGuide.it and Google

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