vsftpd

vsftpd(Very Secure FTP Daemon)는 유닉스와 리눅스에서 사용할 수 있는 가벼운 FTP 서버입니다. 주요 특징은 다음과 같습니다.

• Virtual IP configurations
• Virtual users
• Standalone or inetd operation
• Powerful per-user configurability
• Bandwidth throttling
• Per-source-IP configurability
• Per-source-IP limits
• IPv6
• Encryption support through SSL integration

설치

vsftpd는 우분투 패키지에 포함되어 있으므로 다음과 같이 명령하여 설치할 수 있습니다.

apt install vsftpd

방화벽을 사용 중이라면 다음과 같이 명령하여 포트를 열어줍니다.

ufw allow ftp

주요 기본 설정은 다음과 같습니다.

• 익명 사용자 접속 불가
• 사용자는 읽기 전용으로 접속
• 다른 폴더 보기 가능

설정 파일은 /etc/vsftpd.conf입니다.

# Example config file /etc/vsftpd.conf
#
# The default compiled in settings are fairly paranoid. This sample file
# loosens things up a bit, to make the ftp daemon more usable.
# Please see vsftpd.conf.5 for all compiled in defaults.
#
# READ THIS: This example file is NOT an exhaustive list of vsftpd options.
# Please read the vsftpd.conf.5 manual page to get a full idea of vsftpd's
# capabilities.
#
#
# Run standalone?  vsftpd can run either from an inetd or as a standalone
# daemon started from an initscript.
listen=NO
#
# This directive enables listening on IPv6 sockets. By default, listening
# on the IPv6 "any" address (::) will accept connections from both IPv6
# and IPv4 clients. It is not necessary to listen on *both* IPv4 and IPv6
# sockets. If you want that (perhaps because you want to listen on specific
# addresses) then you must run two copies of vsftpd with two configuration
# files.
listen_ipv6=YES
#
# Allow anonymous FTP? (Disabled by default).
anonymous_enable=NO
#
# Uncomment this to allow local users to log in.
local_enable=YES
#
# Uncomment this to enable any form of FTP write command.
#write_enable=YES
#
# Default umask for local users is 077. You may wish to change this to 022,
# if your users expect that (022 is used by most other ftpd's)
#local_umask=022
#
# Uncomment this to allow the anonymous FTP user to upload files. This only
# has an effect if the above global write enable is activated. Also, you will
# obviously need to create a directory writable by the FTP user.
#anon_upload_enable=YES
#
# Uncomment this if you want the anonymous FTP user to be able to create
# new directories.
#anon_mkdir_write_enable=YES
#
# Activate directory messages - messages given to remote users when they
# go into a certain directory.
dirmessage_enable=YES
#
# If enabled, vsftpd will display directory listings with the time
# in  your  local  time  zone.  The default is to display GMT. The
# times returned by the MDTM FTP command are also affected by this
# option.
use_localtime=YES
#
# Activate logging of uploads/downloads.
xferlog_enable=YES
#
# Make sure PORT transfer connections originate from port 20 (ftp-data).
connect_from_port_20=YES
#
# If you want, you can arrange for uploaded anonymous files to be owned by
# a different user. Note! Using "root" for uploaded files is not
# recommended!
#chown_uploads=YES
#chown_username=whoever
#
# You may override where the log file goes if you like. The default is shown
# below.
#xferlog_file=/var/log/vsftpd.log
#
# If you want, you can have your log file in standard ftpd xferlog format.
# Note that the default log file location is /var/log/xferlog in this case.
#xferlog_std_format=YES
#
# You may change the default value for timing out an idle session.
#idle_session_timeout=600
#
# You may change the default value for timing out a data connection.
#data_connection_timeout=120
#
# It is recommended that you define on your system a unique user which the
# ftp server can use as a totally isolated and unprivileged user.
#nopriv_user=ftpsecure
#
# Enable this and the server will recognise asynchronous ABOR requests. Not
# recommended for security (the code is non-trivial). Not enabling it,
# however, may confuse older FTP clients.
#async_abor_enable=YES
#
# By default the server will pretend to allow ASCII mode but in fact ignore
# the request. Turn on the below options to have the server actually do ASCII
# mangling on files when in ASCII mode.
# Beware that on some FTP servers, ASCII support allows a denial of service
# attack (DoS) via the command "SIZE /big/file" in ASCII mode. vsftpd
# predicted this attack and has always been safe, reporting the size of the
# raw file.
# ASCII mangling is a horrible feature of the protocol.
#ascii_upload_enable=YES
#ascii_download_enable=YES
#
# You may fully customise the login banner string:
#ftpd_banner=Welcome to blah FTP service.
#
# You may specify a file of disallowed anonymous e-mail addresses. Apparently
# useful for combatting certain DoS attacks.
#deny_email_enable=YES
# (default follows)
#banned_email_file=/etc/vsftpd.banned_emails
#
# You may restrict local users to their home directories.  See the FAQ for
# the possible risks in this before using chroot_local_user or
# chroot_list_enable below.
#chroot_local_user=YES
#
# You may specify an explicit list of local users to chroot() to their home
# directory. If chroot_local_user is YES, then this list becomes a list of
# users to NOT chroot().
# (Warning! chroot'ing can be very dangerous. If using chroot, make sure that
# the user does not have write access to the top level directory within the
# chroot)
#chroot_local_user=YES
#chroot_list_enable=YES
# (default follows)
#chroot_list_file=/etc/vsftpd.chroot_list
#
# You may activate the "-R" option to the builtin ls. This is disabled by
# default to avoid remote users being able to cause excessive I/O on large
# sites. However, some broken FTP clients such as "ncftp" and "mirror" assume
# the presence of the "-R" option, so there is a strong case for enabling it.
#ls_recurse_enable=YES
#
# Customization
#
# Some of vsftpd's settings don't fit the filesystem layout by
# default.
#
# This option should be the name of a directory which is empty.  Also, the
# directory should not be writable by the ftp user. This directory is used
# as a secure chroot() jail at times vsftpd does not require filesystem
# access.
secure_chroot_dir=/var/run/vsftpd/empty
#
# This string is the name of the PAM service vsftpd will use.
pam_service_name=vsftpd
#
# This option specifies the location of the RSA certificate to use for SSL
# encrypted connections.
rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
ssl_enable=NO

#
# Uncomment this to indicate that vsftpd use a utf8 filesystem.
#utf8_filesystem=YES서

서버 부팅 시 자동으로 시작하게 하려면 다음과 같이 명령합니다.

systemctl enable vsftpd

설정 변경 후 적용시키려면 서비스를 다시 시작합니다.

systemctl restart vsftpd

주요 설정

사용자 쓰기 가능하게 하기

사용자는 읽기 전용으로 접속하므로 파일을 업로드하거나 삭제하는 것이 불가능합니다. 쓰기 가능하게 하려면 다음 코드에서 주석(#)을 제거합니다.

#write_enable=YES

사용자 홈 디렉토리를 벗어나지 못하게 하기

사용자는 홈 디렉토리를 벗어나서 다른 디렉토리나 파일 목록을 볼 수 있습니다. 다운로드나 업로드는 불가능하나 목록을 보는 거 자체가 문제가 될 수 있습니다. 접속한 사용자가 홈 디렉토리를 벗어나지 못하게 하려면 다음 코드에서 주석을 제거하고...

#chroot_local_user=YES

다음 코드를 추가합니다.

allow_writeable_chroot=YES

익명 사용자 접속

익명 사용자, 즉 누구나 접속할 수 있게 하려면 다음 설정 코드에서 No를...

anonymous_enable=NO

YES로 변경합니다.

anonymous_enable=YES

읽기 전용으로 /srv/ftp에 접속됩니다.

익명 사용자에게 업로드, 쓰기 권한 부여

익명 사용자가 업로드와 쓰기가 가능하게 하려면 두 가지 작업을 해야 합니다.

설정 파일 수정

설정 파일에서 다음 두 코드에서 주석을 제거합니다.

#anon_upload_enable=YES

#anon_mkdir_write_enable=YES

디렉토리 권한 설정

예를 들어 /srv/ftp/pub 디렉토리에 업로드와 쓰기가 가능하게 하고 싶다면, 디렉토리를 만들고...

mkdir /srv/ftp/pub

쓰기 가능하게 권한을 부여하거나...

chmod 777 /srv/ftp/pub

ftp 사용자에게 소유권을 부여합니다.

chown ftp:ftp /srv/ftp/pub