I recently encountered the following error with Singularity 3.7.3 on Arch linux. It used to work for me but now fails:
$ singularity -d run hello.simg
DEBUG [U=1000,P=681364] persistentPreRun() Singularity version: 3.7.3
DEBUG [U=1000,P=681364] persistentPreRun() Parsing configuration file /etc/singularity/singularity.conf
DEBUG [U=1000,P=681364] handleConfDir() /home/alu/.singularity already exists. Not creating.
DEBUG [U=1000,P=681364] execStarter() Saving umask 0022 for propagation into container
DEBUG [U=1000,P=681364] execStarter() Checking for encrypted system partition
DEBUG [U=1000,P=681364] Init() Image format detection
DEBUG [U=1000,P=681364] Init() Check for sandbox image format
DEBUG [U=1000,P=681364] Init() sandbox format initializer returned: not a directory image
DEBUG [U=1000,P=681364] Init() Check for sif image format
DEBUG [U=1000,P=681364] Init() sif format initializer returned: SIF magic not found
DEBUG [U=1000,P=681364] Init() Check for squashfs image format
DEBUG [U=1000,P=681364] Init() squashfs image format detected
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding SHELL environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding SESSION_MANAGER environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding COLORTERM environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LESS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_SESSION_PATH environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_MENU_PREFIX environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding CONDA_EXE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding _CE_M environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding HISTSIZE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding SSH_AUTH_SOCK environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XMODIFIERS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding DESKTOP_SESSION environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LC_MONETARY environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding EDITOR environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding DBUS_STARTER_BUS_TYPE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding PWD environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LOGNAME environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_SESSION_DESKTOP environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding QT_QPA_PLATFORMTHEME environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_SESSION_TYPE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding CONDA_PREFIX environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding MAMBA_ROOT_PREFIX environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding MANPATH environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding SYSTEMD_EXEC_PID environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XAUTHORITY environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_GREETER_DATA_DIR environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding MOTD_SHOWN environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding GDM_LANG environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LC_PAPER environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LANG environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LS_COLORS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_CURRENT_DESKTOP environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding DARWIN environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding VTE_VERSION environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding CONDA_PROMPT_MODIFIER environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_SEAT_PATH environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding MPW_FULLNAME environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding INVOCATION_ID environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding MANAGERPID environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding INFOPATH environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding NVM_DIR environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_SESSION_CLASS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding TERM environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding _CE_CONDA environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding USER environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LIBRARY_PATH environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding MICRO_MYOTIS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding CONDA_SHLVL environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding DISPLAY environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding SHLVL environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding NVM_CD_FLAGS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding PBGAPS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding PAGER environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding QT_IM_MODULE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LC_MEASUREMENT environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding DBUS_STARTER_ADDRESS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding OOO_FORCE_DESKTOP environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding COOKIE_VERIFICATION_SECRET environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding DENTIST environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding CONDA_PYTHON_EXE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding TILIX_ID environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding XDG_RUNTIME_DIR environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding CONDA_DEFAULT_ENV environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LC_TIME environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding JOURNAL_STREAM environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LC_COLLATE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding GTK3_MODULES environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding GDMSESSION environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding HISTFILESIZE environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding DBUS_SESSION_BUS_ADDRESS environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding HG environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding NVM_BIN environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding MAIL environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding LC_NUMERIC environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding OLDPWD environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding _ environment variable
DEBUG [U=1000,P=681364] SetContainerEnv() Forwarding USER_PATH environment variable
VERBOSE [U=1000,P=681364] SetContainerEnv() Setting HOME=/home/alu
VERBOSE [U=1000,P=681364] SetContainerEnv() Setting PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
DEBUG [U=1000,P=681364] init() Use starter binary /usr/lib/singularity/bin/starter-suid
VERBOSE [U=0,P=681364] print() Set messagelevel to: 5
VERBOSE [U=0,P=681364] init() Starter initialization
DEBUG [U=0,P=681364] load_overlay_module() Trying to load overlay kernel module
DEBUG [U=0,P=681364] load_overlay_module() Overlay seems supported by the kernel
VERBOSE [U=0,P=681364] is_suid() Check if we are running as setuid
VERBOSE [U=0,P=681364] priv_drop() Drop root privileges
DEBUG [U=1000,P=681364] read_engine_config() Read engine configuration
DEBUG [U=1000,P=681364] init() Wait completion of stage1
VERBOSE [U=1000,P=681373] priv_drop() Drop root privileges permanently
DEBUG [U=1000,P=681373] set_parent_death_signal() Set parent death signal to 9
VERBOSE [U=1000,P=681373] init() Spawn stage 1
DEBUG [U=1000,P=681373] startup() singularity runtime engine selected
VERBOSE [U=1000,P=681373] startup() Execute stage 1
DEBUG [U=1000,P=681373] StageOne() Entering stage 1
DEBUG [U=1000,P=681373] prepareAutofs() Found "/proc/sys/fs/binfmt_misc" as autofs mount point
DEBUG [U=1000,P=681373] prepareAutofs() Could not keep file descriptor for bind path /etc/localtime: no mount point
DEBUG [U=1000,P=681373] prepareAutofs() Could not keep file descriptor for bind path /etc/hosts: no mount point
DEBUG [U=1000,P=681373] prepareAutofs() Could not keep file descriptor for home directory /home/alu: no mount point
DEBUG [U=1000,P=681373] prepareAutofs() Could not keep file descriptor for current working directory /home/alu/projects/pb-gaps/src/dentist-example: no mount point
DEBUG [U=1000,P=681373] Init() Image format detection
DEBUG [U=1000,P=681373] Init() Check for sandbox image format
DEBUG [U=1000,P=681373] Init() sandbox format initializer returned: not a directory image
DEBUG [U=1000,P=681373] Init() Check for sif image format
DEBUG [U=1000,P=681373] Init() sif format initializer returned: SIF magic not found
DEBUG [U=1000,P=681373] Init() Check for squashfs image format
DEBUG [U=1000,P=681373] Init() squashfs image format detected
DEBUG [U=1000,P=681373] setSessionLayer() Overlay seems supported and allowed by kernel
DEBUG [U=1000,P=681373] setSessionLayer() Attempting to use overlayfs (enable overlay = try)
VERBOSE [U=1000,P=681364] wait_child() stage 1 exited with status 0
DEBUG [U=1000,P=681364] cleanup_fd() Close file descriptor 4
DEBUG [U=1000,P=681364] cleanup_fd() Close file descriptor 5
DEBUG [U=1000,P=681364] cleanup_fd() Close file descriptor 6
DEBUG [U=1000,P=681364] init() Set child signal mask
DEBUG [U=1000,P=681364] init() Create socketpair for master communication channel
DEBUG [U=1000,P=681364] init() Create RPC socketpair for communication between stage 2 and RPC server
VERBOSE [U=1000,P=681364] priv_escalate() Get root privileges
VERBOSE [U=0,P=681364] priv_escalate() Change filesystem uid to 1000
VERBOSE [U=0,P=681364] init() Spawn master process
DEBUG [U=0,P=681379] set_parent_death_signal() Set parent death signal to 9
VERBOSE [U=0,P=681379] create_namespace() Create mount namespace
VERBOSE [U=0,P=681364] enter_namespace() Entering in mount namespace
DEBUG [U=0,P=681364] enter_namespace() Opening namespace file ns/mnt
VERBOSE [U=0,P=681379] create_namespace() Create mount namespace
DEBUG [U=0,P=681364] set_master_privileges() Set master privileges
DEBUG [U=0,P=681364] apply_privileges() Effective capabilities: 0x00000000000000c0
DEBUG [U=0,P=681364] apply_privileges() Permitted capabilities: 0x000001ffffffffff
DEBUG [U=0,P=681364] apply_privileges() Bounding capabilities: 0x000001ffffffffff
DEBUG [U=0,P=681364] apply_privileges() Inheritable capabilities: 0x000001ffffffffff
DEBUG [U=0,P=681364] apply_privileges() Ambient capabilities: 0x0000000000000000
DEBUG [U=0,P=681364] apply_privileges() Set user ID to 1000
DEBUG [U=0,P=681380] set_rpc_privileges() Set RPC privileges
DEBUG [U=0,P=681380] apply_privileges() Effective capabilities: 0x0000000000200000
DEBUG [U=0,P=681380] apply_privileges() Permitted capabilities: 0x000001ffffffffff
DEBUG [U=0,P=681380] apply_privileges() Bounding capabilities: 0x0000000008204000
DEBUG [U=0,P=681380] apply_privileges() Inheritable capabilities: 0x0000000000000000
DEBUG [U=0,P=681380] apply_privileges() Ambient capabilities: 0x0000000000000000
DEBUG [U=0,P=681380] apply_privileges() Set user ID to 1000
DEBUG [U=1000,P=681380] set_parent_death_signal() Set parent death signal to 9
VERBOSE [U=1000,P=681380] init() Spawn RPC server
DEBUG [U=1000,P=681364] startup() singularity runtime engine selected
VERBOSE [U=1000,P=681364] startup() Execute master process
DEBUG [U=1000,P=681380] startup() singularity runtime engine selected
VERBOSE [U=1000,P=681380] startup() Serve RPC requests
DEBUG [U=1000,P=681364] setupSessionLayout() Using Layer system: overlay
DEBUG [U=1000,P=681364] setupOverlayLayout() Creating overlay SESSIONDIR layout
DEBUG [U=1000,P=681364] addRootfsMount() Mount rootfs in read-only mode
DEBUG [U=1000,P=681364] addRootfsMount() Image type is 4096
DEBUG [U=1000,P=681364] addRootfsMount() Mounting block [squashfs] image: /home/alu/projects/pb-gaps/src/dentist-example/hello.simg
DEBUG [U=1000,P=681364] addKernelMount() Checking configuration file for 'mount proc'
DEBUG [U=1000,P=681364] addKernelMount() Adding proc to mount list
VERBOSE [U=1000,P=681364] addKernelMount() Default mount: /proc:/proc
DEBUG [U=1000,P=681364] addKernelMount() Checking configuration file for 'mount sys'
DEBUG [U=1000,P=681364] addKernelMount() Adding sysfs to mount list
VERBOSE [U=1000,P=681364] addKernelMount() Default mount: /sys:/sys
DEBUG [U=1000,P=681364] addDevMount() Checking configuration file for 'mount dev'
DEBUG [U=1000,P=681364] addDevMount() Adding dev to mount list
VERBOSE [U=1000,P=681364] addDevMount() Default mount: /dev:/dev
DEBUG [U=1000,P=681364] addHostMount() Not mounting host file systems per configuration
VERBOSE [U=1000,P=681364] addBindsMount() Found 'bind path' = /etc/localtime, /etc/localtime
VERBOSE [U=1000,P=681364] addBindsMount() Found 'bind path' = /etc/hosts, /etc/hosts
DEBUG [U=1000,P=681364] addHomeStagingDir() Staging home directory (/home/alu) at /var/singularity/mnt/session/home/alu
DEBUG [U=1000,P=681364] addHomeMount() Adding home directory mount [/var/singularity/mnt/session/home/alu:/home/alu] to list using layer: overlay
DEBUG [U=1000,P=681364] addTmpMount() Checking for 'mount tmp' in configuration file
VERBOSE [U=1000,P=681364] addTmpMount() Default mount: /tmp:/tmp
VERBOSE [U=1000,P=681364] addTmpMount() Default mount: /var/tmp:/var/tmp
DEBUG [U=1000,P=681364] addScratchMount() Not mounting scratch directory: Not requested
DEBUG [U=1000,P=681364] addLibsMount() Checking for 'user bind control' in configuration file
DEBUG [U=1000,P=681364] addFilesMount() Checking for 'user bind control' in configuration file
DEBUG [U=1000,P=681364] addResolvConfMount() Adding /etc/resolv.conf to mount list
VERBOSE [U=1000,P=681364] addResolvConfMount() Default mount: /etc/resolv.conf:/etc/resolv.conf
DEBUG [U=1000,P=681364] addHostnameMount() Skipping hostname mount, not virtualizing UTS namespace on user request
DEBUG [U=1000,P=681364] create() Mount all
DEBUG [U=1000,P=681364] mountGeneric() Mounting tmpfs to /var/singularity/mnt/session
FATAL [U=1000,P=681364] Master() container creation failed: mount /proc/self/fd/3->/var/singularity/mnt/session/rootfs error: while mounting image /proc/self/fd/3: failed to find loop device: could not attach image file to loop device: no loop devices available
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
sys on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
dev on /dev type devtmpfs (rw,nosuid,relatime,size=3914504k,nr_inodes=978626,mode=755,inode64)
run on /run type tmpfs (rw,nosuid,nodev,relatime,mode=755,inode64)
/dev/mapper/AntergosVG-AntergosRoot on / type ext4 (rw,noatime,discard)
securityfs on /sys/kernel/security type securityfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev,inode64)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime)
pstore on /sys/fs/pstore type pstore (rw,nosuid,nodev,noexec,relatime)
none on /sys/fs/bpf type bpf (rw,nosuid,nodev,noexec,relatime,mode=700)
systemd-1 on /proc/sys/fs/binfmt_misc type autofs (rw,relatime,fd=30,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=11543)
mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime)
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,pagesize=2M)
debugfs on /sys/kernel/debug type debugfs (rw,nosuid,nodev,noexec,relatime)
tracefs on /sys/kernel/tracing type tracefs (rw,nosuid,nodev,noexec,relatime)
configfs on /sys/kernel/config type configfs (rw,nosuid,nodev,noexec,relatime)
fusectl on /sys/fs/fuse/connections type fusectl (rw,nosuid,nodev,noexec,relatime)
/dev/sda1 on /boot type ext4 (rw,noatime,discard,stripe=4)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,nr_inodes=409600,inode64)
tmpfs on /run/user/1000 type tmpfs (rw,nosuid,nodev,relatime,size=785652k,nr_inodes=196413,mode=700,uid=1000,gid=100,inode64)
gvfsd-fuse on /run/user/1000/gvfs type fuse.gvfsd-fuse (rw,nosuid,nodev,relatime,user_id=1000,group_id=100)
/dev/mmcblk0p1 on /run/media/alu/0BF9-003D type fuseblk (rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096,uhelper=udisks2)