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applications.md

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title: Linux Server Applications breadcrumbs:

  • title: Configuration
  • title: Linux Server --- {% include header.md %}

Using

{:.no_toc} Debian 10 Buster

Docker & Docker Compose

TODO

Setup

  1. Install Docker (Debian).
  2. Install Docker Compose.
  3. Install Docker Compose command completion.
  4. (Optional) Setup swap limit:
    • If docker info contains WARNING: No swap limit support, it's not working and should maybe be fixed.
    • It incurs a small performance degredation and is optional but recommended.
    • In /etc/default/grub, add cgroup_enable=memory swapaccount=1 to GRUB_CMDLINE_LINUX.
    • Run update-grub and reboot.

Docker Compose TMPDIR Fix

Docker Compose will fail to work if /tmp has noexec.

  1. Move /usr/local/bin/docker-compose to /usr/local/bin/docker-compose-normal.
  2. Create /usr/local/bin/docker-compose with the contents below and make it executable.

  3. Create the new TMPDIR dir.

    #!/bin/bash
# Some dir without noexec
export TMPDIR=/var/lib/docker-compose-tmp
/usr/local/bin/docker-compose-normal "$@"

Fail2ban

Setup

  1. Install fail2ban.
  2. Fix the firewall first so it configures itself correctly wrt. firewall blocking.
  3. Check the status with fail2ban-client status [sshd].

ISC DHCP Server and radvd

Notes

  • DHCPv4 uses raw sockets, so it bypasses the firewall (i.e. no firewall rules are needed). DHCPv6, however, does not. This includes the respective clients as well.

Setup

  1. Install and enable isc-dhcp-server and radvd.
  2. Add config files.
    1. DHCPv4: /etc/dhcp/dhcpd.conf
    2. DHCPv6 (optional): /etc/dhcp/dhcpd6.conf
    3. radvd: /etc/radvd.conf
  3. If using systemd-networkd, fix wrong startup order:
    • TODO
  4. IPv4:
    1. Configure DHCPv4.
  5. IPv6:
    1. For SLAAC, configure only radvd.
    2. Dor DHCPv6, configure radvd in stateful mode and DHCPv6.
  6. (Optional) Setup interfaces to listen to:
    • This may mute the "No subnet declaration for ..." verbose error on some distros.
    • In /etc/default/isc-dhcp-server, add the interfaces (space-separated) to INTERFACESv4 and INTERFACESv6.

ntopng

Setup

  1. Install ntopng.
  2. Make sure service ntopng is enabled and running.
  3. Fix log dir owner: chown nobody:nogroup /var/log/ntopng
  4. Configure:
    1. Open /etc/ntopng.conf.
    2. Add -W=<new_port> to enable HTTPS.
    3. (Optional) Set -w=0 to disable HTTP.
  5. Restart it (takes a while).

ntpd

Setup

  1. Disable systemd-timesyncd NTP client by disabling and stopping systemd-timesyncd.
  2. Install ntp.
  3. In /etc/ntp.conf, replace existing servers/pools with ntp.justervesenet.no with the iburst option.
  4. Test with ntpq -pn (it may take a minute to synchronize).

Postfix

Satellite system

Notes

  • When using an SMTP relay, the original IP address will likely be found in the mail headers.
  • Make sure DNS is configured correctly (SPF, DKIM, DMARC).

Setup

  1. Install: postfix libsasl2-modules mailutils
    • If asked, choose to configure Postfix as a satellite system.
  2. Set the FQDN:
    1. Update it in /etc/postfix/main.cf.
    2. Link mailname to hostname (must be FQDN): ln -sf /etc/hostname /etc/mailname
  3. Update the root alias in /etc/aliases and run newaliases.
  4. Update the main.cf config (example not provided here).
    1. Only listen to localhost: Set “inet_interfaces = loopback-only”
    2. Disable relaying: Set “mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128”
    3. Anonymize banner: “smtpd_banner = $myhostname ESMTP”
  5. Relay guides:
    1. Mailgun:
      1. How To Start Sending Email (Mailgun)
      2. How to Set Up a Mail Relay with Postfix and Mailgun on Ubuntu 16.04 (DigitalOcean)
    2. SendGrid:
      1. Postfix (SendGrid)
      2. Use API-key with permission to send mail only.
      3. The API-key username is apikey.
  6. Setup address rewrite rules:
    • For fixing the To and From fields, which is typically from root to root.
    • Add the rewrite config (see example below).
    • Reference the config using smtp_header_checks in the main config.
    • Test: postmap -fq "From: root@<FQDN>" regexp:smtp_header_checks
  7. Setup relay credentials (SASL):
    1. Credentials file: /etc/postfix/sasl_passwd
    2. Add your credentials using format: [relay_domain]:port user@domain:password
    3. Run: postmap sasl_passwd
    4. Fix permissions: chmod 600 sasl_passwd*
  8. Restart postfix.
  9. Try sending an email: echo "Test from $(hostname) at time $(date)." | mail -s "Test" root

Examples

# File: smtp_header_checks

/^From:\s*.*\S+@node\.example\.bet.*.*$/ REPLACE From: "Node" <node@example.net>
/^To:\s*.*\S+@node\.example\.net.*$/ REPLACE To: "Someone" <someone@example.net>

Usage

  • Send a test mail: echo "Test from $HOSTNAME at time $(date)." | mail -s "Test" root
  • Test the config: postconf > /dev/null
  • Print the config: postconf -n
  • If mails are stuck in the mail queue (mailq) because of previous errors, run postqueue -f to flush them.

Pterodactyl

Setup

  • Note: The node must be publicly accessable.
  • Follow the official guide.

Game Servers

CSGO

  • It uses a ton of storage, between 20 and 30 GB last I checked. If you useless, the installer will fail with some useless error message.
  • Use app ID 730 in Steam Game Server Account Manager, regardless of which app ID the server was created with. If you use e.g. 740, the server will not be able to log into Steam.

radvd

See ISC DHCP Server and radvd.

TFTP-HPA

Setup

  1. Install tftpd-hpa.
  2. Update /etc/default/tftpd-hpa based on the config below.
  3. Create the folder /var/tftp with permissions 777 and user-group pair tftp:tftp.
  4. Restart it.
  5. If it shouldn't automatically start, disble it.

Files

# File: /etc/default/tftpd-hpa

TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/var/tftp"
TFTP_ADDRESS=":69"
TFTP_OPTIONS="--create --secure"

Unbound

Setup

  1. Install: unbound dns-root-data
  2. Setup the config: /etc/unbound/unbound.conf
  3. Add hostname variants to /etc/hosts.
  4. Configure it in /etc/resolv.conf:
    1. nameserver 127.0.0.1
    2. search <domain>
    3. domain <domain>
  5. Configure it in /etc/systemd/resolved.conf:
    1. DNSStubListener=no
    2. DNS=127.0.0.1
    3. Restart systemd-resolved.
  6. Test DNSSEC:
    1. drill sigfail.verteiltesysteme.net should give an rcode of SERVFAIL.
    2. drill sigok.verteiltesysteme.net should give an rcode of NOERROR.
  7. Make sure dns-root-data is updating root hints in file /usr/share/dns/root.hints.

Troubleshooting

  • It sometimes stops resolving names and responds with "servfail".
    • I don't know why. Restarting it works.

Notes

  • Use DNS over HTTPS/TLS.
  • Setup private addresses for DNS rebinding prevention.

UniFi

Setup

Using the unofficial Docker image by jacobalberty.

  1. Add a system user named "unifi": useradd -r unifi
  2. Allow the ports through the firewall: See UniFi - Ports Used.
  3. Add a Docker Compose file. See docker-compose.yml.
    • Use host networking mode for L2 adoption to work (if you're not using L3 or SSH adoption).
  4. Start the container, open the webpage and follow the wizard.

ZFS

Info

Features

  • Filesystem and physical storage decoupled
  • Always consistent
  • Intent log
  • Synchronous or asynchronous
  • Everything checksummed
  • Compression
  • Deduplication
  • Encryption
  • Snapshots
  • Copy-on-write (CoW)
  • Clones
  • Caching
  • Log-strucrured filesystem
  • Tunable

Terminology

  • Vdev
  • Zpool
  • Zvol
  • ZFS POSIX Layer (ZPL)
  • ZFS Intent Log (ZIL)
  • Adaptive Replacement Cache (ARC)
  • Dataset

Setup

  1. Enable the contrib and non-free repo areas. (Don't use any backports repo.)
  2. Install (it might give errors): zfs-dkms zfsutils-linux zfs-zed
  3. Load the ZFS module: modprobe zfs
  4. Fix the ZFS install: apt install
  5. Make the import service wait for iSCSI:
    1. cp /lib/systemd/system/zfs-import-cache.zervice /etc/systemd/system
    2. Add After=iscsid.service in /etc/systemd/system/zfs-import-cache.service.
    3. systemctl enable zfs-import-cache.service
  6. Set the max ARC size: echo "options zfs zfs_arc_max=<bytes>" >> /etc/modprobe.d/zfs.conf
    • It should typically be around 15-25% of the physical RAM size on general nodes. It defaults to 50%.
  7. Check that the cron scrub script exists.
    • Typical location: /etc/cron.d/zfsutils-linux
    • If it doesn't exist, add one which runs /usr/lib/zfs-linux/scrub e.g. monthly. It'll scrub all disks.

Usage

  • Create a pool: zpool create -o ashift=<9|12> [level] <drives>+
  • Create an encrypted pool:
    • The procedure is basically the same for encrypted datasets.
    • Children of encrypted datasets can't be unencrypted.
    • The encryption suite can't be changed after creation, but the keyformat can.
    • Using a password: zpool create -O encryption=aes-128-gcm -O keyformat=passphrase ...
    • Using a raw key:
    • Generate the key: dd if=/dev/random of=/root/keys/zfs/<tank> bs=32 count=1
    • Create the pool: zpool create -O encryption=aes-128-gcm -O keyformat=raw -O keylocation=file:///root/keys/zfs/<tank> ...
    • Automatically unlock at boot time: Add and enable zfs-load-keys.service.
    • Reboot and test.
    • Check the key status with zfs get keystatus.
  • Send and receive snapshots:
    • zfs send [-R] <snapshot> and zfs recv <snapshot>.
    • Uses STDOUT.
    • Use zfs get receive_resume_token and zfs send -t <token> to resume an interrupted transfer.
  • View activity: zpool iostat [-v]
  • Clear transient device errors: zpool clear <pool> [device]
  • If a pool is "UNAVAIL", it means it can't be recovered without corrupted data.
  • Replace a device and automatically copy data from the old device or from redundant devices: zpool replace <pool> <device> [new-device]
  • Bring a device online or offline: zpool (online|offline) <pool> <device>
  • Re-add device that got wiped: Take it offline and then online again.

Best Practices and Suggestions

  • As far as possible, use raw disks and HBA disk controllers (or RAID controllers in IT mode).
  • Always use /etc/disk/by-id/X, not /dev/sdX.
  • Always manually set the correct ashift for pools.
    • Should be the log-2 of the physical block/sector size of the device.
    • E.g. 12 for 4kB (Advanced Format (AF), common on HDDs) and 9 for 512B (common on SSDs).
    • Check the physical block size with smartctl -i <dev>.
  • Always enable compression. Generally lz4. Maybe zstd when implemented. Maybe gzip-9 for archiving. Worst case it does nothing.
  • Never use deduplication. It may brick your ZFS server.
  • Generally always use quotas and reservations.
  • Avoid using more than 80% of the available space.
  • Make sure regular automatic scrubs are enabled. There should be a cron job/script or something. Run it e.g. every 2 weeks or monthly.
  • Snapshots are great for increments backups. They're easy to send places too. If the dataset is encrypted then so is the snapshot.

Tuning

  • Use quotas, reservations and compression.
  • Very frequent reads:
    • E.g. for a static web root.
    • Set atime=off to disable updating the access time for files.
  • Database:
    • Disable atime.
    • Use an appropriate recordsize with recordsize=<size>.
    • InnoDB should use 16k for data files and 128k on log files (two datasets).
    • PostgreSQL should use 8k (or 16k) for both data and WAL.
    • Disable caching with primarycache=metadata. DMBSes typically handle caching themselves.
    • For InnoDB.
    • For PostgreSQL if the working set fits in RAM.
    • Disable the ZIL with logbias=throughput to prevent writing twice.
    • For InnoDB and PostgreSQL.
    • Consider not using it for high-traffic applications.
    • PostgreSQL:
    • Use the same dataset for data and logs.
    • Use one dataset per database instance. Requires you to specify it when creating the database.
    • Don't use PostgreSQL checksums or compression.
    • Example: su postgres -c 'initdb --no-locale -E=UTF8 -n -N -D /db/pgdb1'

Troubleshooting

  • zfs-import-cache.service fails to import pools because disks are not found:
    • Set options scsi_mod scan=sync in /etc/modprobe.d/zfs.conf to wait for iSCSI disks to come online before ZFS starts.
    • Add After=iscsid.service to zfs-import-cache.service

Extra Notes

  • ECC memory is recommended but not required. It does not affect data corruption on disk.
  • It does not require large amounts of memory, but more memory allows it to cache more data. A minimum of around 1GB is suggested. Memory caching is termed ARC. By default it's limited to 1/2 of all available RAM. Under memory pressure, it releases some of it to other applications.
  • Compressed ARC is a feature which compresses and checksums the ARC. It's enabled by default.
  • A dedicated disk (e.g. an NVMe SSD) can be used as a secondary read cache. This is termed L2ARC (level 2 ARC). Only frequently accessed blocks are cached. The memory requirement will increase based on the size of the L2ARC. It should only be considered for pools with high read traffic, slow disks and lots of memory available.
  • A dedicated disk (e.g. an NVMe SSD) can be used for the ZFS intent log (ZIL), which is used for synchronized writes. This is termed SLOG (separate intent log). The disk must have low latency, high durability and should preferrably be mirrored for redundancy. It should only be considered for pools with high synchronous write traffic on relatively slow disks.
  • Intel Optane is a perfect choice as both L2ARCs and SLOGs due to its high throughput, low latency and high durability.
  • Some SSD models come with a build-in cache. Make sure it actually flushes it on power loss.
  • ZFS is always consistent, even in case of data loss.
  • Bitrot is real.
    • 4.2% to 34% of SSDs have one UBER (uncorrectable bit error rate) per year.
    • External factors:
    • Temperature.
    • Bus power consumption.
    • Data written by system software.
    • Workload changes due to SSD failure.
  • Early signs of drive failures:
    • zpool status <pool> shows that a scrub has repaired any data.
    • zpool status <pool> shows read, write or checksum errors (all values should be zero).
  • Database conventions:
    • One app per database.
    • Encode the environment and DMBS version into the dataset name, e.g. theapp-prod-pg10.

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